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 $82.46   11.838%   $92.2216   $92.22   $92.20   $92.20  
  Purchase #2 $162.99   10.482%   $180.0746   $180.07   $180.05   $180.10  
  Purchase #3 $73.93   3.451%   $76.4813   $76.48   $76.50   $76.50  
  Purchase #4 $213.32   5.676%   $225.428   $225.43   $225.45   $225.40  
  Purchase #5 $80.99   11.645%   $90.4213   $90.42   $90.40   $90.40  
  Purchase #6 $249.85   7.151%   $267.7168   $267.72   $267.70   $267.70  
  Purchase #7 $58.79   9.771%   $64.5344   $64.53   $64.55   $64.50  
  7 purchase totals = $922.33       $996.8780   $996.87   $996.85   $996.80