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 $38.74   12.679%   $43.6518   $43.65   $43.65   $43.70  
  Purchase #2 $36.83   4.668%   $38.5492   $38.55   $38.55   $38.50  
  Purchase #3 $247.82   6.422%   $263.735   $263.74   $263.75   $263.70  
  Purchase #4 $60.74   4.623%   $63.548   $63.55   $63.55   $63.50  
  Purchase #5 $47.84   7.120%   $51.2462   $51.25   $51.25   $51.20  
  Purchase #6 $59.50   7.552%   $63.9934   $63.99   $64.00   $64.00  
  Purchase #7 $173.56   11.295%   $193.1636   $193.16   $193.15   $193.20  
  7 purchase totals = $665.03       $717.8872   $717.89   $717.90   $717.80