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 $49.90   7.140%   $53.4629   $53.46   $53.45   $53.50  
  Purchase #2 $113.88   6.254%   $121.0021   $121.00   $121.00   $121.00  
  Purchase #3 $125.61   8.673%   $136.5042   $136.50   $136.50   $136.50  
  Purchase #4 $41.92   10.644%   $46.382   $46.38   $46.40   $46.40  
  Purchase #5 $217.40   4.221%   $226.5765   $226.58   $226.60   $226.60  
  Purchase #6 $22.61   3.326%   $23.362   $23.36   $23.35   $23.40  
  Purchase #7 $186.94   10.497%   $206.5631   $206.56   $206.55   $206.60  
  7 purchase totals = $758.26       $813.8528   $813.84   $813.85   $814.00