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 $38.93   9.119%   $42.48   $42.48   $42.50   $42.50  
  Purchase #2 $165.77   12.159%   $185.926   $185.93   $185.95   $185.90  
  Purchase #3 $225.50   6.869%   $240.9896   $240.99   $241.00   $241.00  
  Purchase #4 $119.92   10.366%   $132.3509   $132.35   $132.35   $132.40  
  Purchase #5 $144.84   9.640%   $158.8026   $158.80   $158.80   $158.80  
  Purchase #6 $13.79   7.826%   $14.8692   $14.87   $14.85   $14.90  
  Purchase #7 $224.26   5.458%   $236.5001   $236.50   $236.50   $236.50  
  7 purchase totals = $933.01       $1,011.9184   $1,011.92   $1,011.95   $1,012.00