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 $197.91   6.874%   $211.5143   $211.51   $211.50   $211.50  
  Purchase #2 $198.61   7.248%   $213.0053   $213.01   $213.00   $213.00  
  Purchase #3 $131.79   3.369%   $136.23   $136.23   $136.25   $136.20  
  Purchase #4 $244.99   6.123%   $259.9907   $259.99   $260.00   $260.00  
  Purchase #5 $68.46   11.717%   $76.4815   $76.48   $76.50   $76.50  
  Purchase #6 $204.82   13.185%   $231.8255   $231.83   $231.85   $231.80  
  Purchase #7 $131.54   7.392%   $141.2634   $141.26   $141.25   $141.30  
  7 purchase totals = $1,178.12       $1,270.3107   $1,270.31   $1,270.35   $1,270.30