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 $237.54   6.589%   $253.1915   $253.19   $253.20   $253.20  
  Purchase #2 $24.88   10.333%   $27.4509   $27.45   $27.45   $27.50  
  Purchase #3 $48.64   9.552%   $53.2861   $53.29   $53.30   $53.30  
  Purchase #4 $234.91   6.759%   $250.7876   $250.79   $250.80   $250.80  
  Purchase #5 $78.42   11.294%   $87.2768   $87.28   $87.30   $87.30  
  Purchase #6 $179.57   3.328%   $185.5461   $185.55   $185.55   $185.50  
  Purchase #7 $97.68   13.125%   $110.5005   $110.50   $110.50   $110.50  
  7 purchase totals = $901.64       $968.0395   $968.05   $968.10   $968.10