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 $61.76   8.132%   $66.7823   $66.78   $66.80   $66.80  
  Purchase #2 $44.26   8.295%   $47.9314   $47.93   $47.95   $47.90  
  Purchase #3 $206.48   3.442%   $213.587   $213.59   $213.60   $213.60  
  Purchase #4 $161.57   8.551%   $175.3859   $175.39   $175.40   $175.40  
  Purchase #5 $16.34   8.540%   $17.7354   $17.74   $17.75   $17.70  
  Purchase #6 $173.82   4.352%   $181.3846   $181.38   $181.40   $181.40  
  Purchase #7 $28.52   6.666%   $30.4211   $30.42   $30.40   $30.40  
  7 purchase totals = $692.75       $733.2277   $733.23   $733.30   $733.20