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 $92.59   3.584%   $95.9084   $95.91   $95.90   $95.90  
  Purchase #2 $24.65   4.524%   $25.7652   $25.77   $25.75   $25.80  
  Purchase #3 $166.74   6.727%   $177.9566   $177.96   $177.95   $178.00  
  Purchase #4 $213.88   11.592%   $238.673   $238.67   $238.65   $238.70  
  Purchase #5 $57.89   5.307%   $60.9622   $60.96   $60.95   $61.00  
  Purchase #6 $159.33   9.308%   $174.1604   $174.16   $174.15   $174.20  
  Purchase #7 $164.98   10.813%   $182.8193   $182.82   $182.80   $182.80  
  7 purchase totals = $880.06       $956.2451   $956.25   $956.15   $956.40