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 $56.47   12.673%   $63.6264   $63.63   $63.65   $63.60  
  Purchase #2 $44.62   13.531%   $50.6575   $50.66   $50.65   $50.70  
  Purchase #3 $156.98   5.477%   $165.5778   $165.58   $165.60   $165.60  
  Purchase #4 $44.43   6.576%   $47.3517   $47.35   $47.35   $47.40  
  Purchase #5 $238.50   13.501%   $270.6999   $270.70   $270.70   $270.70  
  Purchase #6 $154.60   5.453%   $163.0303   $163.03   $163.05   $163.00  
  Purchase #7 $23.92   3.800%   $24.829   $24.83   $24.85   $24.80  
  7 purchase totals = $719.52       $785.7726   $785.78   $785.85   $785.80