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 $44.74   13.210%   $50.6502   $50.65   $50.65   $50.70  
  Purchase #2 $111.81   3.357%   $115.5635   $115.56   $115.55   $115.60  
  Purchase #3 $65.70   5.431%   $69.2682   $69.27   $69.25   $69.30  
  Purchase #4 $164.42   6.526%   $175.15   $175.15   $175.15   $175.20  
  Purchase #5 $128.52   11.753%   $143.625   $143.63   $143.65   $143.60  
  Purchase #6 $71.68   10.795%   $79.4179   $79.42   $79.40   $79.40  
  Purchase #7 $124.79   11.350%   $138.9537   $138.95   $138.95   $139.00  
  7 purchase totals = $711.66       $772.6285   $772.63   $772.60   $772.80