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 $156.46   6.699%   $166.9413   $166.94   $166.95   $166.90  
  Purchase #2 $198.87   6.559%   $211.9139   $211.91   $211.90   $211.90  
  Purchase #3 $53.72   6.624%   $57.2784   $57.28   $57.30   $57.30  
  Purchase #4 $82.81   4.274%   $86.3493   $86.35   $86.35   $86.30  
  Purchase #5 $246.62   7.303%   $264.6307   $264.63   $264.65   $264.60  
  Purchase #6 $61.52   11.602%   $68.6576   $68.66   $68.65   $68.70  
  Purchase #7 $11.30   8.142%   $12.22   $12.22   $12.20   $12.20  
  7 purchase totals = $811.30       $867.9912   $867.99   $868.00   $867.90