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 $116.33   11.180%   $129.3357   $129.34   $129.35   $129.30  
  Purchase #2 $63.47   10.368%   $70.0506   $70.05   $70.05   $70.10  
  Purchase #3 $91.85   6.538%   $97.8552   $97.86   $97.85   $97.90  
  Purchase #4 $208.55   7.697%   $224.6021   $224.60   $224.60   $224.60  
  Purchase #5 $111.35   3.676%   $115.4432   $115.44   $115.45   $115.40  
  Purchase #6 $243.93   12.572%   $274.5969   $274.60   $274.60   $274.60  
  Purchase #7 $102.89   8.737%   $111.8795   $111.88   $111.90   $111.90  
  7 purchase totals = $938.37       $1,023.7632   $1,023.77   $1,023.80   $1,023.80