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 $243.40   8.487%   $264.0574   $264.06   $264.05   $264.10  
  Purchase #2 $176.96   7.176%   $189.6586   $189.66   $189.65   $189.70  
  Purchase #3 $154.47   3.555%   $159.9614   $159.96   $159.95   $160.00  
  Purchase #4 $55.70   5.543%   $58.7875   $58.79   $58.80   $58.80  
  Purchase #5 $23.48   9.135%   $25.6249   $25.62   $25.60   $25.60  
  Purchase #6 $36.72   8.690%   $39.911   $39.91   $39.90   $39.90  
  Purchase #7 $206.69   8.577%   $224.4178   $224.42   $224.40   $224.40  
  7 purchase totals = $897.42       $962.4186   $962.42   $962.35   $962.50