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 $22.87   7.299%   $24.5393   $24.54   $24.55   $24.50  
  Purchase #2 $85.78   10.240%   $94.5639   $94.56   $94.55   $94.60  
  Purchase #3 $237.73   3.535%   $246.1338   $246.13   $246.15   $246.10  
  Purchase #4 $160.40   8.872%   $174.6307   $174.63   $174.65   $174.60  
  Purchase #5 $177.44   9.669%   $194.5967   $194.60   $194.60   $194.60  
  Purchase #6 $190.37   12.487%   $214.1415   $214.14   $214.15   $214.10  
  Purchase #7 $121.92   5.741%   $128.9194   $128.92   $128.90   $128.90  
  7 purchase totals = $996.51       $1,077.5253   $1,077.52   $1,077.55   $1,077.40