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 $38.63   12.393%   $43.4174   $43.42   $43.40   $43.40  
  Purchase #2 $124.92   7.213%   $133.9305   $133.93   $133.95   $133.90  
  Purchase #3 $186.79   11.675%   $208.5977   $208.60   $208.60   $208.60  
  Purchase #4 $6.72   7.273%   $7.2087   $7.21   $7.20   $7.20  
  Purchase #5 $244.82   13.412%   $277.6553   $277.66   $277.65   $277.70  
  Purchase #6 $169.93   8.308%   $184.0478   $184.05   $184.05   $184.00  
  Purchase #7 $87.38   9.208%   $95.426   $95.43   $95.45   $95.40  
  7 purchase totals = $859.19       $950.2834   $950.30   $950.30   $950.20