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 $112.99   5.117%   $118.7717   $118.77   $118.75   $118.80  
  Purchase #2 $170.91   4.717%   $178.9718   $178.97   $178.95   $179.00  
  Purchase #3 $205.61   13.797%   $233.978   $233.98   $234.00   $234.00  
  Purchase #4 $190.62   3.574%   $197.4328   $197.43   $197.45   $197.40  
  Purchase #5 $118.62   13.571%   $134.7179   $134.72   $134.70   $134.70  
  Purchase #6 $69.77   4.855%   $73.1573   $73.16   $73.15   $73.20  
  Purchase #7 $202.62   5.293%   $213.3447   $213.34   $213.35   $213.30  
  7 purchase totals = $1,071.14       $1,150.3742   $1,150.37   $1,150.35   $1,150.40