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 $54.25   11.683%   $60.588   $60.59   $60.60   $60.60  
  Purchase #2 $122.68   7.343%   $131.6884   $131.69   $131.70   $131.70  
  Purchase #3 $90.54   4.222%   $94.3626   $94.36   $94.35   $94.40  
  Purchase #4 $114.54   8.508%   $124.2851   $124.29   $124.30   $124.30  
  Purchase #5 $20.31   8.794%   $22.0961   $22.10   $22.10   $22.10  
  Purchase #6 $244.48   11.531%   $272.671   $272.67   $272.65   $272.70  
  Purchase #7 $125.78   11.122%   $139.7693   $139.77   $139.75   $139.80  
  7 purchase totals = $772.58       $845.4605   $845.47   $845.45   $845.60