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 $92.67   3.390%   $95.8115   $95.81   $95.80   $95.80  
  Purchase #2 $182.69   3.150%   $188.4447   $188.44   $188.45   $188.40  
  Purchase #3 $238.48   5.805%   $252.3238   $252.32   $252.30   $252.30  
  Purchase #4 $46.31   7.147%   $49.6198   $49.62   $49.60   $49.60  
  Purchase #5 $8.39   3.239%   $8.6618   $8.66   $8.65   $8.70  
  Purchase #6 $52.66   3.180%   $54.3346   $54.33   $54.35   $54.30  
  Purchase #7 $115.62   8.492%   $125.4385   $125.44   $125.45   $125.40  
  7 purchase totals = $736.82       $774.6347   $774.62   $774.60   $774.50