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 $235.65   11.486%   $262.7168   $262.72   $262.70   $262.70  
  Purchase #2 $83.83   6.136%   $88.9738   $88.97   $88.95   $89.00  
  Purchase #3 $15.36   6.727%   $16.3933   $16.39   $16.40   $16.40  
  Purchase #4 $72.67   4.478%   $75.9242   $75.92   $75.90   $75.90  
  Purchase #5 $91.44   7.862%   $98.629   $98.63   $98.65   $98.60  
  Purchase #6 $217.93   12.658%   $245.5156   $245.52   $245.50   $245.50  
  Purchase #7 $213.90   10.422%   $236.1927   $236.19   $236.20   $236.20  
  7 purchase totals = $930.78       $1,024.3454   $1,024.34   $1,024.30   $1,024.30