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 $61.26   7.353%   $65.7644   $65.76   $65.75   $65.80  
  Purchase #2 $191.53   6.462%   $203.9067   $203.91   $203.90   $203.90  
  Purchase #3 $23.79   12.124%   $26.6743   $26.67   $26.65   $26.70  
  Purchase #4 $53.25   5.676%   $56.2725   $56.27   $56.25   $56.30  
  Purchase #5 $35.64   3.632%   $36.9344   $36.93   $36.95   $36.90  
  Purchase #6 $242.50   10.248%   $267.3514   $267.35   $267.35   $267.40  
  Purchase #7 $79.89   9.138%   $87.1903   $87.19   $87.20   $87.20  
  7 purchase totals = $687.86       $744.0940   $744.08   $744.05   $744.20