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 $43.34   6.114%   $45.9898   $45.99   $46.00   $46.00  
  Purchase #2 $119.62   13.724%   $136.0366   $136.04   $136.05   $136.00  
  Purchase #3 $204.71   13.610%   $232.571   $232.57   $232.55   $232.60  
  Purchase #4 $249.25   13.792%   $283.6266   $283.63   $283.65   $283.60  
  Purchase #5 $100.61   9.844%   $110.514   $110.51   $110.50   $110.50  
  Purchase #6 $222.78   9.250%   $243.3872   $243.39   $243.40   $243.40  
  Purchase #7 $192.34   3.657%   $199.3739   $199.37   $199.35   $199.40  
  7 purchase totals = $1,132.65       $1,251.4991   $1,251.50   $1,251.50   $1,251.50