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 $57.68   9.528%   $63.1758   $63.18   $63.20   $63.20  
  Purchase #2 $129.59   10.854%   $143.6557   $143.66   $143.65   $143.70  
  Purchase #3 $114.78   10.202%   $126.4899   $126.49   $126.50   $126.50  
  Purchase #4 $135.42   9.326%   $148.0493   $148.05   $148.05   $148.00  
  Purchase #5 $60.82   5.778%   $64.3342   $64.33   $64.35   $64.30  
  Purchase #6 $121.72   3.391%   $125.8475   $125.85   $125.85   $125.80  
  Purchase #7 $246.58   5.220%   $259.4515   $259.45   $259.45   $259.50  
  7 purchase totals = $866.59       $931.0039   $931.01   $931.05   $931.00