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 $185.56   11.514%   $206.9254   $206.93   $206.95   $206.90  
  Purchase #2 $108.31   9.832%   $118.959   $118.96   $118.95   $119.00  
  Purchase #3 $88.63   7.208%   $95.0185   $95.02   $95.00   $95.00  
  Purchase #4 $198.73   13.733%   $226.0216   $226.02   $226.00   $226.00  
  Purchase #5 $131.79   5.269%   $138.734   $138.73   $138.75   $138.70  
  Purchase #6 $128.55   9.224%   $140.4075   $140.41   $140.40   $140.40  
  Purchase #7 $16.40   13.841%   $18.6699   $18.67   $18.65   $18.70  
  7 purchase totals = $857.97       $944.7359   $944.74   $944.70   $944.70