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 $67.57   11.327%   $75.2237   $75.22   $75.20   $75.20  
  Purchase #2 $54.29   13.491%   $61.6143   $61.61   $61.60   $61.60  
  Purchase #3 $132.81   9.399%   $145.2928   $145.29   $145.30   $145.30  
  Purchase #4 $57.69   13.311%   $65.3691   $65.37   $65.35   $65.40  
  Purchase #5 $63.81   3.186%   $65.843   $65.84   $65.85   $65.80  
  Purchase #6 $20.74   11.798%   $23.1869   $23.19   $23.20   $23.20  
  Purchase #7 $20.83   11.466%   $23.2184   $23.22   $23.20   $23.20  
  7 purchase totals = $417.74       $459.7482   $459.74   $459.70   $459.70