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 $242.75   6.532%   $258.6064   $258.61   $258.60   $258.60  
  Purchase #2 $167.38   3.651%   $173.491   $173.49   $173.50   $173.50  
  Purchase #3 $24.33   13.840%   $27.6973   $27.70   $27.70   $27.70  
  Purchase #4 $46.29   13.702%   $52.6327   $52.63   $52.65   $52.60  
  Purchase #5 $202.91   7.594%   $218.319   $218.32   $218.30   $218.30  
  Purchase #6 $20.69   4.245%   $21.5683   $21.57   $21.55   $21.60  
  Purchase #7 $186.46   4.174%   $194.2428   $194.24   $194.25   $194.20  
  7 purchase totals = $890.81       $946.5575   $946.56   $946.55   $946.50