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 $187.87   12.325%   $211.025   $211.03   $211.05   $211.00  
  Purchase #2 $48.49   9.533%   $53.1126   $53.11   $53.10   $53.10  
  Purchase #3 $92.77   9.462%   $101.5479   $101.55   $101.55   $101.50  
  Purchase #4 $226.34   13.685%   $257.3146   $257.31   $257.30   $257.30  
  Purchase #5 $229.45   9.762%   $251.8489   $251.85   $251.85   $251.80  
  Purchase #6 $16.92   12.363%   $19.0118   $19.01   $19.00   $19.00  
  Purchase #7 $85.87   7.872%   $92.6297   $92.63   $92.65   $92.60  
  7 purchase totals = $887.71       $986.4905   $986.49   $986.50   $986.30