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 $215.33   5.216%   $226.5616   $226.56   $226.55   $226.60  
  Purchase #2 $51.27   3.321%   $52.9727   $52.97   $52.95   $53.00  
  Purchase #3 $82.34   11.284%   $91.6312   $91.63   $91.65   $91.60  
  Purchase #4 $114.87   4.505%   $120.0449   $120.04   $120.05   $120.00  
  Purchase #5 $185.39   7.491%   $199.2776   $199.28   $199.30   $199.30  
  Purchase #6 $37.62   4.535%   $39.3261   $39.33   $39.35   $39.30  
  Purchase #7 $200.29   12.420%   $225.166   $225.17   $225.15   $225.20  
  7 purchase totals = $887.11       $954.9801   $954.98   $955.00   $955.00