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 $6.84   9.426%   $7.4847   $7.48   $7.50   $7.50  
  Purchase #2 $245.26   10.803%   $271.7554   $271.76   $271.75   $271.80  
  Purchase #3 $85.63   5.390%   $90.2455   $90.25   $90.25   $90.20  
  Purchase #4 $58.84   7.551%   $63.283   $63.28   $63.30   $63.30  
  Purchase #5 $111.89   11.423%   $124.6712   $124.67   $124.65   $124.70  
  Purchase #6 $128.92   6.238%   $136.962   $136.96   $136.95   $137.00  
  Purchase #7 $235.36   8.512%   $255.3938   $255.39   $255.40   $255.40  
  7 purchase totals = $872.74       $949.7956   $949.79   $949.80   $949.90