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 $146.62   4.138%   $152.6871   $152.69   $152.70   $152.70  
  Purchase #2 $57.63   6.799%   $61.5483   $61.55   $61.55   $61.50  
  Purchase #3 $12.95   10.140%   $14.2631   $14.26   $14.25   $14.30  
  Purchase #4 $174.94   7.767%   $188.5276   $188.53   $188.55   $188.50  
  Purchase #5 $93.84   4.831%   $98.3734   $98.37   $98.35   $98.40  
  Purchase #6 $162.35   12.607%   $182.8175   $182.82   $182.80   $182.80  
  Purchase #7 $224.95   3.561%   $232.9605   $232.96   $232.95   $233.00  
  7 purchase totals = $873.28       $931.1775   $931.18   $931.15   $931.20