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 $71.53   7.305%   $76.7553   $76.76   $76.75   $76.80  
  Purchase #2 $239.79   5.567%   $253.1391   $253.14   $253.15   $253.10  
  Purchase #3 $148.42   7.723%   $159.8825   $159.88   $159.90   $159.90  
  Purchase #4 $63.76   8.146%   $68.9539   $68.95   $68.95   $69.00  
  Purchase #5 $200.97   4.791%   $210.5985   $210.60   $210.60   $210.60  
  Purchase #6 $214.58   5.705%   $226.8218   $226.82   $226.80   $226.80  
  Purchase #7 $119.52   3.518%   $123.7247   $123.72   $123.70   $123.70  
  7 purchase totals = $1,058.57       $1,119.8758   $1,119.87   $1,119.85   $1,119.90