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 $85.35   9.608%   $93.5504   $93.55   $93.55   $93.60  
  Purchase #2 $52.73   5.463%   $55.6106   $55.61   $55.60   $55.60  
  Purchase #3 $29.89   6.298%   $31.7725   $31.77   $31.75   $31.80  
  Purchase #4 $109.74   4.162%   $114.3074   $114.31   $114.30   $114.30  
  Purchase #5 $204.73   5.814%   $216.633   $216.63   $216.65   $216.60  
  Purchase #6 $166.39   10.520%   $183.8942   $183.89   $183.90   $183.90  
  Purchase #7 $177.72   7.618%   $191.2587   $191.26   $191.25   $191.30  
  7 purchase totals = $826.55       $887.0268   $887.02   $887.00   $887.10