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 $157.59   3.169%   $162.584   $162.58   $162.60   $162.60  
  Purchase #2 $69.85   9.684%   $76.6143   $76.61   $76.60   $76.60  
  Purchase #3 $171.74   5.418%   $181.0449   $181.04   $181.05   $181.00  
  Purchase #4 $218.54   12.730%   $246.3601   $246.36   $246.35   $246.40  
  Purchase #5 $124.59   12.749%   $140.474   $140.47   $140.45   $140.50  
  Purchase #6 $232.91   7.528%   $250.4435   $250.44   $250.45   $250.40  
  Purchase #7 $119.34   9.767%   $130.9959   $131.00   $131.00   $131.00  
  7 purchase totals = $1,094.56       $1,188.5167   $1,188.50   $1,188.50   $1,188.50