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 $248.68   10.692%   $275.2689   $275.27   $275.25   $275.30  
  Purchase #2 $119.35   6.147%   $126.6864   $126.69   $126.70   $126.70  
  Purchase #3 $207.80   4.452%   $217.0513   $217.05   $217.05   $217.10  
  Purchase #4 $225.79   4.477%   $235.8986   $235.90   $235.90   $235.90  
  Purchase #5 $93.43   4.307%   $97.454   $97.45   $97.45   $97.50  
  Purchase #6 $105.32   10.316%   $116.1848   $116.18   $116.20   $116.20  
  Purchase #7 $196.83   4.642%   $205.9668   $205.97   $205.95   $206.00  
  7 purchase totals = $1,197.20       $1,274.5108   $1,274.51   $1,274.50   $1,274.70