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 $143.28   8.723%   $155.7783   $155.78   $155.80   $155.80  
  Purchase #2 $81.75   7.422%   $87.8175   $87.82   $87.80   $87.80  
  Purchase #3 $169.27   3.811%   $175.7209   $175.72   $175.70   $175.70  
  Purchase #4 $129.72   10.442%   $143.2654   $143.27   $143.25   $143.30  
  Purchase #5 $40.28   3.678%   $41.7615   $41.76   $41.75   $41.80  
  Purchase #6 $103.28   13.423%   $117.1433   $117.14   $117.15   $117.10  
  Purchase #7 $44.96   9.279%   $49.1318   $49.13   $49.15   $49.10  
  7 purchase totals = $712.54       $770.6187   $770.62   $770.60   $770.60