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 $242.62   11.219%   $269.8395   $269.84   $269.85   $269.80  
  Purchase #2 $173.96   11.708%   $194.3272   $194.33   $194.35   $194.30  
  Purchase #3 $8.55   12.655%   $9.632   $9.63   $9.65   $9.60  
  Purchase #4 $142.34   5.410%   $150.0406   $150.04   $150.05   $150.00  
  Purchase #5 $193.71   6.123%   $205.5709   $205.57   $205.55   $205.60  
  Purchase #6 $69.27   10.397%   $76.472   $76.47   $76.45   $76.50  
  Purchase #7 $111.55   3.616%   $115.5836   $115.58   $115.60   $115.60  
  7 purchase totals = $942.00       $1,021.4658   $1,021.46   $1,021.50   $1,021.40