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 $155.99   10.307%   $172.0679   $172.07   $172.05   $172.10  
  Purchase #2 $118.49   6.292%   $125.9454   $125.95   $125.95   $125.90  
  Purchase #3 $226.98   10.723%   $251.3191   $251.32   $251.30   $251.30  
  Purchase #4 $59.73   8.614%   $64.8751   $64.88   $64.90   $64.90  
  Purchase #5 $139.74   9.507%   $153.0251   $153.03   $153.05   $153.00  
  Purchase #6 $249.94   12.734%   $281.7674   $281.77   $281.75   $281.80  
  Purchase #7 $120.50   5.386%   $126.9901   $126.99   $127.00   $127.00  
  7 purchase totals = $1,071.37       $1,175.9901   $1,176.01   $1,176.00   $1,176.00