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 $88.57   8.759%   $96.3278   $96.33   $96.35   $96.30  
  Purchase #2 $169.49   13.728%   $192.7576   $192.76   $192.75   $192.80  
  Purchase #3 $156.91   4.603%   $164.1326   $164.13   $164.15   $164.10  
  Purchase #4 $153.38   5.186%   $161.3343   $161.33   $161.35   $161.30  
  Purchase #5 $169.29   8.734%   $184.0758   $184.08   $184.10   $184.10  
  Purchase #6 $79.62   11.337%   $88.6465   $88.65   $88.65   $88.60  
  Purchase #7 $46.92   8.553%   $50.9331   $50.93   $50.95   $50.90  
  7 purchase totals = $864.18       $938.2077   $938.21   $938.30   $938.10