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 $69.67   5.488%   $73.4935   $73.49   $73.50   $73.50  
  Purchase #2 $239.79   10.611%   $265.2341   $265.23   $265.25   $265.20  
  Purchase #3 $67.73   3.790%   $70.297   $70.30   $70.30   $70.30  
  Purchase #4 $129.60   5.710%   $137.0002   $137.00   $137.00   $137.00  
  Purchase #5 $95.48   6.731%   $101.9068   $101.91   $101.90   $101.90  
  Purchase #6 $84.52   8.369%   $91.5935   $91.59   $91.60   $91.60  
  Purchase #7 $129.47   12.747%   $145.9735   $145.97   $145.95   $146.00  
  7 purchase totals = $816.26       $885.4986   $885.49   $885.50   $885.50