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 $59.34   7.807%   $63.9727   $63.97   $63.95   $64.00  
  Purchase #2 $16.68   12.290%   $18.73   $18.73   $18.75   $18.70  
  Purchase #3 $61.41   11.330%   $68.3678   $68.37   $68.35   $68.40  
  Purchase #4 $250.59   8.632%   $272.2209   $272.22   $272.20   $272.20  
  Purchase #5 $173.58   7.146%   $185.984   $185.98   $186.00   $186.00  
  Purchase #6 $147.60   7.106%   $158.0885   $158.09   $158.10   $158.10  
  Purchase #7 $235.34   8.315%   $254.9085   $254.91   $254.90   $254.90  
  7 purchase totals = $944.54       $1,022.2724   $1,022.27   $1,022.25   $1,022.30