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 $58.45   3.629%   $60.5712   $60.57   $60.55   $60.60  
  Purchase #2 $197.75   7.552%   $212.6841   $212.68   $212.70   $212.70  
  Purchase #3 $233.68   13.555%   $265.3553   $265.36   $265.35   $265.40  
  Purchase #4 $49.38   6.775%   $52.7255   $52.73   $52.75   $52.70  
  Purchase #5 $168.70   5.814%   $178.5082   $178.51   $178.50   $178.50  
  Purchase #6 $207.46   8.649%   $225.4032   $225.40   $225.40   $225.40  
  Purchase #7 $221.27   11.684%   $247.1232   $247.12   $247.10   $247.10  
  7 purchase totals = $1,136.69       $1,242.3707   $1,242.37   $1,242.35   $1,242.40