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 $34.75   3.664%   $36.0232   $36.02   $36.00   $36.00  
  Purchase #2 $173.91   11.779%   $194.3949   $194.39   $194.40   $194.40  
  Purchase #3 $245.50   9.244%   $268.194   $268.19   $268.20   $268.20  
  Purchase #4 $213.83   12.633%   $240.8431   $240.84   $240.85   $240.80  
  Purchase #5 $21.63   10.412%   $23.8821   $23.88   $23.90   $23.90  
  Purchase #6 $152.96   12.365%   $171.8735   $171.87   $171.85   $171.90  
  Purchase #7 $58.34   11.843%   $65.2492   $65.25   $65.25   $65.20  
  7 purchase totals = $900.92       $1,000.4600   $1,000.44   $1,000.45   $1,000.40