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 $114.60   11.380%   $127.6415   $127.64   $127.65   $127.60  
  Purchase #2 $149.67   10.720%   $165.7146   $165.71   $165.70   $165.70  
  Purchase #3 $134.78   11.195%   $149.8686   $149.87   $149.85   $149.90  
  Purchase #4 $226.79   13.505%   $257.418   $257.42   $257.40   $257.40  
  Purchase #5 $238.49   3.681%   $247.2688   $247.27   $247.25   $247.30  
  Purchase #6 $192.33   11.843%   $215.1076   $215.11   $215.10   $215.10  
  Purchase #7 $95.98   5.616%   $101.3702   $101.37   $101.35   $101.40  
  7 purchase totals = $1,152.64       $1,264.3893   $1,264.39   $1,264.30   $1,264.40