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 $236.60   13.256%   $267.9637   $267.96   $267.95   $268.00  
  Purchase #2 $220.42   6.822%   $235.4571   $235.46   $235.45   $235.50  
  Purchase #3 $86.99   6.749%   $92.861   $92.86   $92.85   $92.90  
  Purchase #4 $245.25   9.328%   $268.1269   $268.13   $268.15   $268.10  
  Purchase #5 $240.46   13.164%   $272.1142   $272.11   $272.10   $272.10  
  Purchase #6 $49.75   7.398%   $53.4305   $53.43   $53.45   $53.40  
  Purchase #7 $122.40   6.713%   $130.6167   $130.62   $130.60   $130.60  
  7 purchase totals = $1,201.87       $1,320.5701   $1,320.57   $1,320.55   $1,320.60