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 $180.62   11.563%   $201.5051   $201.51   $201.50   $201.50  
  Purchase #2 $178.61   9.177%   $195.001   $195.00   $195.00   $195.00  
  Purchase #3 $14.87   13.191%   $16.8315   $16.83   $16.85   $16.80  
  Purchase #4 $189.30   10.435%   $209.0535   $209.05   $209.05   $209.10  
  Purchase #5 $186.53   12.507%   $209.8593   $209.86   $209.85   $209.90  
  Purchase #6 $239.89   3.130%   $247.3986   $247.40   $247.40   $247.40  
  Purchase #7 $221.51   6.620%   $236.174   $236.17   $236.15   $236.20  
  7 purchase totals = $1,211.33       $1,315.8230   $1,315.82   $1,315.80   $1,315.90