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 $242.60   10.109%   $267.1244   $267.12   $267.10   $267.10  
  Purchase #2 $109.73   6.486%   $116.8471   $116.85   $116.85   $116.80  
  Purchase #3 $41.33   11.359%   $46.0247   $46.02   $46.00   $46.00  
  Purchase #4 $228.51   7.366%   $245.342   $245.34   $245.35   $245.30  
  Purchase #5 $178.48   7.854%   $192.4978   $192.50   $192.50   $192.50  
  Purchase #6 $219.30   13.445%   $248.7849   $248.78   $248.80   $248.80  
  Purchase #7 $141.38   12.462%   $158.9988   $159.00   $159.00   $159.00  
  7 purchase totals = $1,161.33       $1,275.6197   $1,275.61   $1,275.60   $1,275.50