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 $102.37   3.227%   $105.6735   $105.67   $105.65   $105.70  
  Purchase #2 $218.98   6.853%   $233.9867   $233.99   $234.00   $234.00  
  Purchase #3 $20.28   3.788%   $21.0482   $21.05   $21.05   $21.00  
  Purchase #4 $108.69   3.363%   $112.3452   $112.35   $112.35   $112.30  
  Purchase #5 $96.38   8.808%   $104.8692   $104.87   $104.85   $104.90  
  Purchase #6 $150.93   6.158%   $160.2243   $160.22   $160.20   $160.20  
  Purchase #7 $7.81   10.416%   $8.6235   $8.62   $8.60   $8.60  
  7 purchase totals = $705.44       $746.7706   $746.77   $746.70   $746.70