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 $87.95   11.857%   $98.3782   $98.38   $98.40   $98.40  
  Purchase #2 $10.41   8.136%   $11.257   $11.26   $11.25   $11.30  
  Purchase #3 $169.47   3.859%   $176.0098   $176.01   $176.00   $176.00  
  Purchase #4 $185.44   9.518%   $203.0902   $203.09   $203.10   $203.10  
  Purchase #5 $59.98   5.826%   $63.4744   $63.47   $63.45   $63.50  
  Purchase #6 $34.48   8.863%   $37.536   $37.54   $37.55   $37.50  
  Purchase #7 $239.52   6.482%   $255.0457   $255.05   $255.05   $255.00  
  7 purchase totals = $787.25       $844.7913   $844.80   $844.80   $844.80