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 $96.89   10.180%   $106.7534   $106.75   $106.75   $106.80  
  Purchase #2 $23.73   13.454%   $26.9226   $26.92   $26.90   $26.90  
  Purchase #3 $83.29   4.761%   $87.2554   $87.26   $87.25   $87.30  
  Purchase #4 $151.29   11.515%   $168.711   $168.71   $168.70   $168.70  
  Purchase #5 $241.29   11.161%   $268.2204   $268.22   $268.20   $268.20  
  Purchase #6 $108.30   8.381%   $117.3766   $117.38   $117.40   $117.40  
  Purchase #7 $167.77   10.155%   $184.807   $184.81   $184.80   $184.80  
  7 purchase totals = $872.56       $960.0464   $960.05   $960.00   $960.10