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 $62.35   4.166%   $64.9475   $64.95   $64.95   $64.90  
  Purchase #2 $121.93   6.686%   $130.0822   $130.08   $130.10   $130.10  
  Purchase #3 $145.31   13.544%   $164.9908   $164.99   $165.00   $165.00  
  Purchase #4 $13.45   12.358%   $15.1122   $15.11   $15.10   $15.10  
  Purchase #5 $70.67   8.217%   $76.477   $76.48   $76.50   $76.50  
  Purchase #6 $246.47   7.659%   $265.3471   $265.35   $265.35   $265.30  
  Purchase #7 $194.84   11.217%   $216.6952   $216.70   $216.70   $216.70  
  7 purchase totals = $855.02       $933.6520   $933.66   $933.70   $933.60