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 $92.88   3.191%   $95.8438   $95.84   $95.85   $95.80  
  Purchase #2 $50.93   10.379%   $56.216   $56.22   $56.20   $56.20  
  Purchase #3 $58.90   9.514%   $64.5037   $64.50   $64.50   $64.50  
  Purchase #4 $24.27   4.212%   $25.2923   $25.29   $25.30   $25.30  
  Purchase #5 $229.57   12.630%   $258.5647   $258.56   $258.55   $258.60  
  Purchase #6 $248.88   7.431%   $267.3743   $267.37   $267.35   $267.40  
  Purchase #7 $45.58   13.378%   $51.6777   $51.68   $51.70   $51.70  
  7 purchase totals = $751.01       $819.4725   $819.46   $819.45   $819.50