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 $45.86   13.234%   $51.9291   $51.93   $51.95   $51.90  
  Purchase #2 $216.86   7.267%   $232.6192   $232.62   $232.60   $232.60  
  Purchase #3 $126.57   7.439%   $135.9855   $135.99   $136.00   $136.00  
  Purchase #4 $185.28   13.747%   $210.7504   $210.75   $210.75   $210.80  
  Purchase #5 $194.63   11.433%   $216.882   $216.88   $216.90   $216.90  
  Purchase #6 $235.42   11.781%   $263.1548   $263.15   $263.15   $263.20  
  Purchase #7 $168.52   8.311%   $182.5257   $182.53   $182.55   $182.50  
  7 purchase totals = $1,173.14       $1,293.8467   $1,293.85   $1,293.90   $1,293.90