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 $69.76   6.513%   $74.3035   $74.30   $74.30   $74.30  
  Purchase #2 $40.46   5.349%   $42.6242   $42.62   $42.60   $42.60  
  Purchase #3 $28.49   7.688%   $30.6803   $30.68   $30.70   $30.70  
  Purchase #4 $218.92   6.178%   $232.4449   $232.44   $232.45   $232.40  
  Purchase #5 $207.28   9.751%   $227.4919   $227.49   $227.50   $227.50  
  Purchase #6 $54.29   5.854%   $57.4681   $57.47   $57.45   $57.50  
  Purchase #7 $67.91   12.574%   $76.449   $76.45   $76.45   $76.40  
  7 purchase totals = $687.11       $741.4619   $741.45   $741.45   $741.40