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 $82.74   12.187%   $92.8235   $92.82   $92.80   $92.80  
  Purchase #2 $111.27   10.867%   $123.3617   $123.36   $123.35   $123.40  
  Purchase #3 $234.75   13.705%   $266.9225   $266.92   $266.90   $266.90  
  Purchase #4 $17.53   7.630%   $18.8675   $18.87   $18.85   $18.90  
  Purchase #5 $236.56   13.750%   $269.087   $269.09   $269.10   $269.10  
  Purchase #6 $195.25   12.419%   $219.4981   $219.50   $219.50   $219.50  
  Purchase #7 $116.38   11.513%   $129.7788   $129.78   $129.80   $129.80  
  7 purchase totals = $994.48       $1,120.3391   $1,120.34   $1,120.30   $1,120.40