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 $119.72   3.805%   $124.2753   $124.28   $124.30   $124.30  
  Purchase #2 $23.64   12.620%   $26.6234   $26.62   $26.60   $26.60  
  Purchase #3 $60.93   12.751%   $68.6992   $68.70   $68.70   $68.70  
  Purchase #4 $192.58   13.859%   $219.2697   $219.27   $219.25   $219.30  
  Purchase #5 $204.66   8.744%   $222.5555   $222.56   $222.55   $222.60  
  Purchase #6 $171.38   11.195%   $190.566   $190.57   $190.55   $190.60  
  Purchase #7 $55.49   5.468%   $58.5242   $58.52   $58.50   $58.50  
  7 purchase totals = $828.40       $910.5133   $910.52   $910.45   $910.60