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 $53.96   8.234%   $58.4031   $58.40   $58.40   $58.40  
  Purchase #2 $113.32   5.672%   $119.7475   $119.75   $119.75   $119.70  
  Purchase #3 $248.43   9.553%   $272.1625   $272.16   $272.15   $272.20  
  Purchase #4 $92.52   3.497%   $95.7554   $95.76   $95.75   $95.80  
  Purchase #5 $170.90   12.573%   $192.3873   $192.39   $192.40   $192.40  
  Purchase #6 $173.36   11.328%   $192.9982   $193.00   $193.00   $193.00  
  Purchase #7 $185.78   4.492%   $194.1252   $194.13   $194.15   $194.10  
  7 purchase totals = $1,038.27       $1,125.5792   $1,125.59   $1,125.60   $1,125.60