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 $29.46   9.414%   $32.2334   $32.23   $32.25   $32.20  
  Purchase #2 $202.47   11.383%   $225.5172   $225.52   $225.50   $225.50  
  Purchase #3 $206.30   5.652%   $217.9601   $217.96   $217.95   $218.00  
  Purchase #4 $42.77   9.782%   $46.9538   $46.95   $46.95   $47.00  
  Purchase #5 $72.95   12.597%   $82.1395   $82.14   $82.15   $82.10  
  Purchase #6 $151.28   5.687%   $159.8833   $159.88   $159.90   $159.90  
  Purchase #7 $245.65   13.770%   $279.476   $279.48   $279.50   $279.50  
  7 purchase totals = $950.88       $1,044.1633   $1,044.16   $1,044.20   $1,044.20