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 $235.71   3.764%   $244.5821   $244.58   $244.60   $244.60  
  Purchase #2 $212.38   7.793%   $228.9308   $228.93   $228.95   $228.90  
  Purchase #3 $244.96   8.424%   $265.5954   $265.60   $265.60   $265.60  
  Purchase #4 $167.40   11.334%   $186.3731   $186.37   $186.35   $186.40  
  Purchase #5 $217.93   13.623%   $247.6186   $247.62   $247.60   $247.60  
  Purchase #6 $217.67   8.674%   $236.5507   $236.55   $236.55   $236.60  
  Purchase #7 $72.62   7.446%   $78.0273   $78.03   $78.05   $78.00  
  7 purchase totals = $1,368.67       $1,487.6780   $1,487.68   $1,487.70   $1,487.70