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 $63.39   8.793%   $68.9639   $68.96   $68.95   $69.00  
  Purchase #2 $96.62   8.517%   $104.8491   $104.85   $104.85   $104.80  
  Purchase #3 $194.55   13.541%   $220.894   $220.89   $220.90   $220.90  
  Purchase #4 $15.37   9.758%   $16.8698   $16.87   $16.85   $16.90  
  Purchase #5 $139.56   7.597%   $150.1624   $150.16   $150.15   $150.20  
  Purchase #6 $167.76   8.648%   $182.2679   $182.27   $182.25   $182.30  
  Purchase #7 $149.60   6.843%   $159.8371   $159.84   $159.85   $159.80  
  7 purchase totals = $826.85       $903.8442   $903.84   $903.80   $903.90