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 $241.45   10.734%   $267.3672   $267.37   $267.35   $267.40  
  Purchase #2 $144.48   10.494%   $159.6417   $159.64   $159.65   $159.60  
  Purchase #3 $228.94   5.613%   $241.7904   $241.79   $241.80   $241.80  
  Purchase #4 $135.97   6.458%   $144.7509   $144.75   $144.75   $144.80  
  Purchase #5 $15.68   6.848%   $16.7538   $16.75   $16.75   $16.80  
  Purchase #6 $169.91   3.581%   $175.9945   $175.99   $176.00   $176.00  
  Purchase #7 $243.29   6.859%   $259.9773   $259.98   $260.00   $260.00  
  7 purchase totals = $1,179.72       $1,266.2758   $1,266.27   $1,266.30   $1,266.40