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 $80.82   6.701%   $86.2357   $86.24   $86.25   $86.20  
  Purchase #2 $247.66   8.537%   $268.8027   $268.80   $268.80   $268.80  
  Purchase #3 $136.87   3.695%   $141.9273   $141.93   $141.95   $141.90  
  Purchase #4 $115.62   12.601%   $130.1893   $130.19   $130.20   $130.20  
  Purchase #5 $150.80   7.323%   $161.8431   $161.84   $161.85   $161.80  
  Purchase #6 $157.45   12.503%   $177.136   $177.14   $177.15   $177.10  
  Purchase #7 $45.97   4.727%   $48.143   $48.14   $48.15   $48.10  
  7 purchase totals = $935.19       $1,014.2771   $1,014.28   $1,014.35   $1,014.10