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 $81.46   8.277%   $88.2024   $88.20   $88.20   $88.20  
  Purchase #2 $111.43   7.326%   $119.5934   $119.59   $119.60   $119.60  
  Purchase #3 $33.80   3.136%   $34.86   $34.86   $34.85   $34.90  
  Purchase #4 $55.65   3.707%   $57.7129   $57.71   $57.70   $57.70  
  Purchase #5 $32.94   3.507%   $34.0952   $34.10   $34.10   $34.10  
  Purchase #6 $200.55   8.485%   $217.5667   $217.57   $217.55   $217.60  
  Purchase #7 $179.50   13.446%   $203.6356   $203.64   $203.65   $203.60  
  7 purchase totals = $695.33       $755.6662   $755.67   $755.65   $755.70