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 $69.63   8.754%   $75.7254   $75.73   $75.75   $75.70  
  Purchase #2 $215.56   9.668%   $236.4003   $236.40   $236.40   $236.40  
  Purchase #3 $56.30   13.816%   $64.0784   $64.08   $64.10   $64.10  
  Purchase #4 $63.34   7.407%   $68.0316   $68.03   $68.05   $68.00  
  Purchase #5 $68.44   7.275%   $73.419   $73.42   $73.40   $73.40  
  Purchase #6 $22.42   7.388%   $24.0764   $24.08   $24.10   $24.10  
  Purchase #7 $160.68   8.732%   $174.7106   $174.71   $174.70   $174.70  
  7 purchase totals = $656.37       $716.4417   $716.45   $716.50   $716.40