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 $242.96   13.204%   $275.0404   $275.04   $275.05   $275.00  
  Purchase #2 $100.56   3.172%   $103.7498   $103.75   $103.75   $103.70  
  Purchase #3 $64.91   3.196%   $66.9845   $66.98   $67.00   $67.00  
  Purchase #4 $101.83   6.827%   $108.7819   $108.78   $108.80   $108.80  
  Purchase #5 $159.41   11.340%   $177.4871   $177.49   $177.50   $177.50  
  Purchase #6 $10.65   12.564%   $11.9881   $11.99   $12.00   $12.00  
  Purchase #7 $119.48   4.548%   $124.914   $124.91   $124.90   $124.90  
  7 purchase totals = $799.80       $868.9458   $868.94   $869.00   $868.90