Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $192.30   5.372%   $202.6304   $202.63   $202.65   $202.60  
  Purchase #2 $190.54   3.335%   $196.8945   $196.89   $196.90   $196.90  
  Purchase #3 $155.52   13.511%   $176.5323   $176.53   $176.55   $176.50  
  Purchase #4 $138.54   13.735%   $157.5685   $157.57   $157.55   $157.60  
  Purchase #5 $246.29   3.591%   $255.1343   $255.13   $255.15   $255.10  
  Purchase #6 $128.83   13.514%   $146.2401   $146.24   $146.25   $146.20  
  Purchase #7 $209.34   13.643%   $237.9003   $237.90   $237.90   $237.90  
  7 purchase totals = $1,261.36       $1,372.9004   $1,372.89   $1,372.95   $1,372.80