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 $74.61   6.727%   $79.629   $79.63   $79.65   $79.60  
  Purchase #2 $93.35   5.638%   $98.6131   $98.61   $98.60   $98.60  
  Purchase #3 $71.43   3.827%   $74.1636   $74.16   $74.15   $74.20  
  Purchase #4 $248.82   12.698%   $280.4152   $280.42   $280.40   $280.40  
  Purchase #5 $103.38   10.208%   $113.933   $113.93   $113.95   $113.90  
  Purchase #6 $96.44   13.435%   $109.3967   $109.40   $109.40   $109.40  
  Purchase #7 $169.35   6.640%   $180.5948   $180.59   $180.60   $180.60  
  7 purchase totals = $857.38       $936.7454   $936.74   $936.75   $936.70