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 $67.59   9.361%   $73.9171   $73.92   $73.90   $73.90  
  Purchase #2 $80.80   5.616%   $85.3377   $85.34   $85.35   $85.30  
  Purchase #3 $67.68   12.860%   $76.3836   $76.38   $76.40   $76.40  
  Purchase #4 $79.93   8.836%   $86.9926   $86.99   $87.00   $87.00  
  Purchase #5 $172.89   6.515%   $184.1538   $184.15   $184.15   $184.20  
  Purchase #6 $247.67   11.134%   $275.2456   $275.25   $275.25   $275.20  
  Purchase #7 $160.71   7.753%   $173.1698   $173.17   $173.15   $173.20  
  7 purchase totals = $877.27       $955.2002   $955.20   $955.20   $955.20