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 $168.26   9.776%   $184.7091   $184.71   $184.70   $184.70  
  Purchase #2 $105.83   5.396%   $111.5406   $111.54   $111.55   $111.50  
  Purchase #3 $61.34   5.356%   $64.6254   $64.63   $64.65   $64.60  
  Purchase #4 $206.68   9.319%   $225.9405   $225.94   $225.95   $225.90  
  Purchase #5 $183.46   10.745%   $203.1728   $203.17   $203.15   $203.20  
  Purchase #6 $190.96   3.359%   $197.3743   $197.37   $197.35   $197.40  
  Purchase #7 $213.43   3.640%   $221.1989   $221.20   $221.20   $221.20  
  7 purchase totals = $1,129.96       $1,208.5616   $1,208.56   $1,208.55   $1,208.50