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 $195.64   5.668%   $206.7289   $206.73   $206.75   $206.70  
  Purchase #2 $9.90   12.108%   $11.0987   $11.10   $11.10   $11.10  
  Purchase #3 $34.45   3.593%   $35.6878   $35.69   $35.70   $35.70  
  Purchase #4 $116.98   4.315%   $122.0277   $122.03   $122.05   $122.00  
  Purchase #5 $182.87   12.247%   $205.2661   $205.27   $205.25   $205.30  
  Purchase #6 $50.67   5.757%   $53.5871   $53.59   $53.60   $53.60  
  Purchase #7 $37.39   5.678%   $39.513   $39.51   $39.50   $39.50  
  7 purchase totals = $627.90       $673.9093   $673.92   $673.95   $673.90