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 $132.48   6.803%   $141.4926   $141.49   $141.50   $141.50  
  Purchase #2 $214.25   5.682%   $226.4237   $226.42   $226.40   $226.40  
  Purchase #3 $244.73   11.434%   $272.7124   $272.71   $272.70   $272.70  
  Purchase #4 $155.91   12.627%   $175.5968   $175.60   $175.60   $175.60  
  Purchase #5 $137.55   13.766%   $156.4851   $156.49   $156.50   $156.50  
  Purchase #6 $19.67   6.138%   $20.8773   $20.88   $20.90   $20.90  
  Purchase #7 $203.97   5.529%   $215.2475   $215.25   $215.25   $215.20  
  7 purchase totals = $1,108.56       $1,208.8354   $1,208.84   $1,208.85   $1,208.80