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 $240.97   11.784%   $269.3659   $269.37   $269.35   $269.40  
  Purchase #2 $20.93   6.297%   $22.248   $22.25   $22.25   $22.20  
  Purchase #3 $47.87   5.856%   $50.6733   $50.67   $50.65   $50.70  
  Purchase #4 $192.99   6.510%   $205.5536   $205.55   $205.55   $205.60  
  Purchase #5 $138.67   7.626%   $149.245   $149.25   $149.25   $149.20  
  Purchase #6 $192.40   9.402%   $210.4894   $210.49   $210.50   $210.50  
  Purchase #7 $151.86   11.503%   $169.3285   $169.33   $169.35   $169.30  
  7 purchase totals = $985.69       $1,076.9037   $1,076.91   $1,076.90   $1,076.90