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 $232.57   12.872%   $262.5064   $262.51   $262.50   $262.50  
  Purchase #2 $49.78   13.385%   $56.4431   $56.44   $56.45   $56.40  
  Purchase #3 $132.60   7.292%   $142.2692   $142.27   $142.25   $142.30  
  Purchase #4 $151.86   3.730%   $157.5244   $157.52   $157.50   $157.50  
  Purchase #5 $56.60   9.729%   $62.1066   $62.11   $62.10   $62.10  
  Purchase #6 $188.91   11.717%   $211.0446   $211.04   $211.05   $211.00  
  Purchase #7 $69.88   9.122%   $76.2545   $76.25   $76.25   $76.30  
  7 purchase totals = $882.20       $968.1488   $968.14   $968.10   $968.10