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 $59.74   6.611%   $63.6894   $63.69   $63.70   $63.70  
  Purchase #2 $6.38   12.129%   $7.1538   $7.15   $7.15   $7.20  
  Purchase #3 $159.99   4.678%   $167.4743   $167.47   $167.45   $167.50  
  Purchase #4 $71.85   12.120%   $80.5582   $80.56   $80.55   $80.60  
  Purchase #5 $95.81   8.497%   $103.951   $103.95   $103.95   $104.00  
  Purchase #6 $158.35   7.323%   $169.946   $169.95   $169.95   $169.90  
  Purchase #7 $25.63   3.416%   $26.5055   $26.51   $26.50   $26.50  
  7 purchase totals = $577.75       $619.2782   $619.28   $619.25   $619.40