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 $67.71   12.201%   $75.9713   $75.97   $75.95   $76.00  
  Purchase #2 $167.88   12.147%   $188.2724   $188.27   $188.25   $188.30  
  Purchase #3 $49.94   7.400%   $53.6356   $53.64   $53.65   $53.60  
  Purchase #4 $91.39   7.256%   $98.0213   $98.02   $98.00   $98.00  
  Purchase #5 $45.33   11.691%   $50.6295   $50.63   $50.65   $50.60  
  Purchase #6 $166.91   7.301%   $179.0961   $179.10   $179.10   $179.10  
  Purchase #7 $105.40   7.563%   $113.3714   $113.37   $113.35   $113.40  
  7 purchase totals = $694.56       $758.9976   $759.00   $758.95   $759.00