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 $61.86   13.674%   $70.3187   $70.32   $70.30   $70.30  
  Purchase #2 $242.34   13.443%   $274.9178   $274.92   $274.90   $274.90  
  Purchase #3 $129.43   13.834%   $147.3353   $147.34   $147.35   $147.30  
  Purchase #4 $45.84   11.842%   $51.2684   $51.27   $51.25   $51.30  
  Purchase #5 $50.64   5.128%   $53.2368   $53.24   $53.25   $53.20  
  Purchase #6 $208.33   4.256%   $217.1965   $217.20   $217.20   $217.20  
  Purchase #7 $120.62   7.683%   $129.8872   $129.89   $129.90   $129.90  
  7 purchase totals = $859.06       $944.1607   $944.18   $944.15   $944.10