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 $108.61   13.362%   $123.1225   $123.12   $123.10   $123.10  
  Purchase #2 $246.68   11.245%   $274.4192   $274.42   $274.40   $274.40  
  Purchase #3 $110.44   6.518%   $117.6385   $117.64   $117.65   $117.60  
  Purchase #4 $46.58   13.666%   $52.9456   $52.95   $52.95   $52.90  
  Purchase #5 $204.77   6.436%   $217.949   $217.95   $217.95   $217.90  
  Purchase #6 $232.80   12.464%   $261.8162   $261.82   $261.80   $261.80  
  Purchase #7 $146.68   13.697%   $166.7708   $166.77   $166.75   $166.80  
  7 purchase totals = $1,096.56       $1,214.6618   $1,214.67   $1,214.60   $1,214.50