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 $63.44   3.492%   $65.6553   $65.66   $65.65   $65.70  
  Purchase #2 $119.58   12.424%   $134.4366   $134.44   $134.45   $134.40  
  Purchase #3 $175.42   11.518%   $195.6249   $195.62   $195.60   $195.60  
  Purchase #4 $22.95   4.195%   $23.9128   $23.91   $23.90   $23.90  
  Purchase #5 $99.67   10.329%   $109.9649   $109.96   $109.95   $110.00  
  Purchase #6 $101.73   13.313%   $115.2733   $115.27   $115.25   $115.30  
  Purchase #7 $169.80   7.228%   $182.0731   $182.07   $182.05   $182.10  
  7 purchase totals = $752.59       $826.9409   $826.93   $826.85   $827.00