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 $57.32   9.134%   $62.5556   $62.56   $62.55   $62.60  
  Purchase #2 $136.48   3.516%   $141.2786   $141.28   $141.30   $141.30  
  Purchase #3 $75.90   11.748%   $84.8167   $84.82   $84.80   $84.80  
  Purchase #4 $98.34   5.193%   $103.4468   $103.45   $103.45   $103.40  
  Purchase #5 $188.98   8.119%   $204.3233   $204.32   $204.30   $204.30  
  Purchase #6 $106.52   6.320%   $113.2521   $113.25   $113.25   $113.30  
  Purchase #7 $53.92   13.264%   $61.0719   $61.07   $61.05   $61.10  
  7 purchase totals = $717.46       $770.7450   $770.75   $770.70   $770.80