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 $69.44   8.397%   $75.2709   $75.27   $75.25   $75.30  
  Purchase #2 $141.31   6.633%   $150.6831   $150.68   $150.70   $150.70  
  Purchase #3 $13.77   6.796%   $14.7058   $14.71   $14.70   $14.70  
  Purchase #4 $244.78   12.132%   $274.4767   $274.48   $274.50   $274.50  
  Purchase #5 $107.79   9.791%   $118.3437   $118.34   $118.35   $118.30  
  Purchase #6 $162.26   8.410%   $175.9061   $175.91   $175.90   $175.90  
  Purchase #7 $12.39   4.820%   $12.9872   $12.99   $13.00   $13.00  
  7 purchase totals = $751.74       $822.3735   $822.38   $822.40   $822.40