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 $236.65   8.163%   $255.9677   $255.97   $255.95   $256.00  
  Purchase #2 $11.29   3.153%   $11.646   $11.65   $11.65   $11.60  
  Purchase #3 $207.43   8.566%   $225.1985   $225.20   $225.20   $225.20  
  Purchase #4 $183.50   12.689%   $206.7843   $206.78   $206.80   $206.80  
  Purchase #5 $104.79   12.486%   $117.8741   $117.87   $117.85   $117.90  
  Purchase #6 $97.49   6.241%   $103.5744   $103.57   $103.55   $103.60  
  Purchase #7 $95.43   7.807%   $102.8802   $102.88   $102.90   $102.90  
  7 purchase totals = $936.58       $1,023.9252   $1,023.92   $1,023.90   $1,024.00