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 $145.35   11.627%   $162.2498   $162.25   $162.25   $162.20  
  Purchase #2 $156.82   10.595%   $173.4351   $173.44   $173.45   $173.40  
  Purchase #3 $57.71   7.304%   $61.9251   $61.93   $61.95   $61.90  
  Purchase #4 $245.80   5.397%   $259.0658   $259.07   $259.05   $259.10  
  Purchase #5 $7.58   12.332%   $8.5148   $8.51   $8.50   $8.50  
  Purchase #6 $248.50   6.784%   $265.3582   $265.36   $265.35   $265.40  
  Purchase #7 $57.26   10.337%   $63.179   $63.18   $63.20   $63.20  
  7 purchase totals = $919.02       $993.7278   $993.74   $993.75   $993.70