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 $216.92   11.164%   $241.1369   $241.14   $241.15   $241.10  
  Purchase #2 $164.45   7.412%   $176.639   $176.64   $176.65   $176.60  
  Purchase #3 $54.27   11.363%   $60.4367   $60.44   $60.45   $60.40  
  Purchase #4 $209.94   7.714%   $226.1348   $226.13   $226.15   $226.10  
  Purchase #5 $220.79   10.292%   $243.5137   $243.51   $243.50   $243.50  
  Purchase #6 $180.42   5.228%   $189.8524   $189.85   $189.85   $189.90  
  Purchase #7 $238.86   4.559%   $249.7496   $249.75   $249.75   $249.70  
  7 purchase totals = $1,285.65       $1,387.4631   $1,387.46   $1,387.50   $1,387.30