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 $24.83   5.451%   $26.1835   $26.18   $26.20   $26.20  
  Purchase #2 $145.77   10.686%   $161.347   $161.35   $161.35   $161.30  
  Purchase #3 $211.58   4.504%   $221.1096   $221.11   $221.10   $221.10  
  Purchase #4 $210.42   4.764%   $220.4444   $220.44   $220.45   $220.40  
  Purchase #5 $13.38   10.680%   $14.809   $14.81   $14.80   $14.80  
  Purchase #6 $85.61   12.647%   $96.4371   $96.44   $96.45   $96.40  
  Purchase #7 $52.64   3.794%   $54.6372   $54.64   $54.65   $54.60  
  7 purchase totals = $744.23       $794.9678   $794.97   $795.00   $794.80