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 $66.52   4.133%   $69.2693   $69.27   $69.25   $69.30  
  Purchase #2 $209.35   8.232%   $226.5837   $226.58   $226.60   $226.60  
  Purchase #3 $53.80   13.295%   $60.9527   $60.95   $60.95   $61.00  
  Purchase #4 $74.95   7.809%   $80.8028   $80.80   $80.80   $80.80  
  Purchase #5 $110.69   11.291%   $123.188   $123.19   $123.20   $123.20  
  Purchase #6 $98.63   11.782%   $110.2506   $110.25   $110.25   $110.30  
  Purchase #7 $233.86   8.537%   $253.8246   $253.82   $253.80   $253.80  
  7 purchase totals = $847.80       $924.8717   $924.86   $924.85   $925.00