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 $64.96   12.687%   $73.2015   $73.20   $73.20   $73.20  
  Purchase #2 $151.53   5.819%   $160.3475   $160.35   $160.35   $160.30  
  Purchase #3 $180.72   4.484%   $188.8235   $188.82   $188.80   $188.80  
  Purchase #4 $94.77   11.702%   $105.86   $105.86   $105.85   $105.90  
  Purchase #5 $23.27   12.359%   $26.1459   $26.15   $26.15   $26.10  
  Purchase #6 $100.73   3.687%   $104.4439   $104.44   $104.45   $104.40  
  Purchase #7 $213.48   6.110%   $226.5236   $226.52   $226.50   $226.50  
  7 purchase totals = $829.46       $885.3459   $885.34   $885.30   $885.20