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 $247.42   10.534%   $273.4832   $273.48   $273.50   $273.50  
  Purchase #2 $27.39   7.243%   $29.3739   $29.37   $29.35   $29.40  
  Purchase #3 $160.64   9.815%   $176.4068   $176.41   $176.40   $176.40  
  Purchase #4 $219.52   11.742%   $245.296   $245.30   $245.30   $245.30  
  Purchase #5 $121.26   4.673%   $126.9265   $126.93   $126.95   $126.90  
  Purchase #6 $17.87   10.534%   $19.7524   $19.75   $19.75   $19.80  
  Purchase #7 $125.60   5.259%   $132.2053   $132.21   $132.20   $132.20  
  7 purchase totals = $919.70       $1,003.4441   $1,003.45   $1,003.45   $1,003.50