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 $88.80   5.390%   $93.5863   $93.59   $93.60   $93.60  
  Purchase #2 $185.34   4.224%   $193.1688   $193.17   $193.15   $193.20  
  Purchase #3 $56.77   6.606%   $60.5202   $60.52   $60.50   $60.50  
  Purchase #4 $208.38   7.860%   $224.7587   $224.76   $224.75   $224.80  
  Purchase #5 $178.67   8.125%   $193.1869   $193.19   $193.20   $193.20  
  Purchase #6 $103.35   5.390%   $108.9206   $108.92   $108.90   $108.90  
  Purchase #7 $166.27   9.856%   $182.6576   $182.66   $182.65   $182.70  
  7 purchase totals = $987.58       $1,056.7991   $1,056.81   $1,056.75   $1,056.90