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 $69.82   7.424%   $75.0034   $75.00   $75.00   $75.00  
  Purchase #2 $250.91   5.581%   $264.9133   $264.91   $264.90   $264.90  
  Purchase #3 $104.93   9.855%   $115.2709   $115.27   $115.25   $115.30  
  Purchase #4 $169.59   3.292%   $175.1729   $175.17   $175.15   $175.20  
  Purchase #5 $86.38   11.853%   $96.6186   $96.62   $96.60   $96.60  
  Purchase #6 $123.47   9.382%   $135.054   $135.05   $135.05   $135.10  
  Purchase #7 $15.62   8.175%   $16.8969   $16.90   $16.90   $16.90  
  7 purchase totals = $820.72       $878.9300   $878.92   $878.85   $879.00