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 $48.87   5.297%   $51.4586   $51.46   $51.45   $51.50  
  Purchase #2 $236.96   5.825%   $250.7629   $250.76   $250.75   $250.80  
  Purchase #3 $105.44   6.353%   $112.1386   $112.14   $112.15   $112.10  
  Purchase #4 $103.97   11.694%   $116.1283   $116.13   $116.15   $116.10  
  Purchase #5 $211.96   10.486%   $234.1861   $234.19   $234.20   $234.20  
  Purchase #6 $233.89   4.155%   $243.6081   $243.61   $243.60   $243.60  
  Purchase #7 $17.43   6.149%   $18.5018   $18.50   $18.50   $18.50  
  7 purchase totals = $958.52       $1,026.7844   $1,026.79   $1,026.80   $1,026.80