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 $61.30   13.658%   $69.6724   $69.67   $69.65   $69.70  
  Purchase #2 $117.55   5.421%   $123.9224   $123.92   $123.90   $123.90  
  Purchase #3 $215.68   5.829%   $228.252   $228.25   $228.25   $228.30  
  Purchase #4 $125.77   4.721%   $131.7076   $131.71   $131.70   $131.70  
  Purchase #5 $61.53   9.132%   $67.1489   $67.15   $67.15   $67.10  
  Purchase #6 $155.79   7.681%   $167.7562   $167.76   $167.75   $167.80  
  Purchase #7 $9.33   8.226%   $10.0975   $10.10   $10.10   $10.10  
  7 purchase totals = $746.95       $798.5570   $798.56   $798.50   $798.60