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 $111.93   10.843%   $124.0666   $124.07   $124.05   $124.10  
  Purchase #2 $16.27   7.192%   $17.4401   $17.44   $17.45   $17.40  
  Purchase #3 $118.31   6.705%   $126.2427   $126.24   $126.25   $126.20  
  Purchase #4 $90.80   4.707%   $95.074   $95.07   $95.05   $95.10  
  Purchase #5 $21.62   13.797%   $24.6029   $24.60   $24.60   $24.60  
  Purchase #6 $93.84   11.372%   $104.5115   $104.51   $104.50   $104.50  
  Purchase #7 $238.82   10.796%   $264.603   $264.60   $264.60   $264.60  
  7 purchase totals = $691.59       $756.5408   $756.53   $756.50   $756.50