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 $61.34   11.510%   $68.4002   $68.40   $68.40   $68.40  
  Purchase #2 $216.84   3.692%   $224.8457   $224.85   $224.85   $224.80  
  Purchase #3 $15.26   12.625%   $17.1866   $17.19   $17.20   $17.20  
  Purchase #4 $207.78   4.373%   $216.8662   $216.87   $216.85   $216.90  
  Purchase #5 $215.62   4.616%   $225.573   $225.57   $225.55   $225.60  
  Purchase #6 $120.59   7.176%   $129.2435   $129.24   $129.25   $129.20  
  Purchase #7 $6.88   8.322%   $7.4526   $7.45   $7.45   $7.50  
  7 purchase totals = $844.31       $889.5678   $889.57   $889.55   $889.60