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 $245.56   8.471%   $266.3614   $266.36   $266.35   $266.40  
  Purchase #2 $108.76   8.800%   $118.3309   $118.33   $118.35   $118.30  
  Purchase #3 $186.60   10.465%   $206.1277   $206.13   $206.15   $206.10  
  Purchase #4 $247.39   6.249%   $262.8494   $262.85   $262.85   $262.80  
  Purchase #5 $120.71   3.540%   $124.9831   $124.98   $125.00   $125.00  
  Purchase #6 $157.65   7.313%   $169.1789   $169.18   $169.20   $169.20  
  Purchase #7 $82.67   7.535%   $88.8992   $88.90   $88.90   $88.90  
  7 purchase totals = $1,149.34       $1,236.7306   $1,236.73   $1,236.80   $1,236.70