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 $187.83   11.140%   $208.7543   $208.75   $208.75   $208.80  
  Purchase #2 $112.45   10.742%   $124.5294   $124.53   $124.55   $124.50  
  Purchase #3 $10.66   3.673%   $11.0515   $11.05   $11.05   $11.10  
  Purchase #4 $38.96   8.176%   $42.1454   $42.15   $42.15   $42.10  
  Purchase #5 $208.36   6.618%   $222.1493   $222.15   $222.15   $222.10  
  Purchase #6 $190.38   11.460%   $212.1975   $212.20   $212.20   $212.20  
  Purchase #7 $11.80   7.350%   $12.6673   $12.67   $12.65   $12.70  
  7 purchase totals = $760.44       $833.4947   $833.50   $833.50   $833.50