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 $53.80   13.870%   $61.2621   $61.26   $61.25   $61.30  
  Purchase #2 $227.63   4.824%   $238.6109   $238.61   $238.60   $238.60  
  Purchase #3 $163.77   6.635%   $174.6361   $174.64   $174.65   $174.60  
  Purchase #4 $237.58   4.391%   $248.0121   $248.01   $248.00   $248.00  
  Purchase #5 $88.53   3.195%   $91.3585   $91.36   $91.35   $91.40  
  Purchase #6 $71.44   3.330%   $73.819   $73.82   $73.80   $73.80  
  Purchase #7 $118.76   8.774%   $129.18   $129.18   $129.20   $129.20  
  7 purchase totals = $961.51       $1,016.8787   $1,016.88   $1,016.85   $1,016.90