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 $164.91   11.352%   $183.6306   $183.63   $183.65   $183.60  
  Purchase #2 $84.71   10.641%   $93.724   $93.72   $93.70   $93.70  
  Purchase #3 $117.45   4.143%   $122.316   $122.32   $122.30   $122.30  
  Purchase #4 $246.30   6.803%   $263.0558   $263.06   $263.05   $263.10  
  Purchase #5 $160.66   6.285%   $170.7575   $170.76   $170.75   $170.80  
  Purchase #6 $178.38   13.582%   $202.6076   $202.61   $202.60   $202.60  
  Purchase #7 $157.63   7.775%   $169.8857   $169.89   $169.90   $169.90  
  7 purchase totals = $1,110.04       $1,205.9772   $1,205.99   $1,205.95   $1,206.00