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 $184.47   3.384%   $190.7125   $190.71   $190.70   $190.70  
  Purchase #2 $84.91   11.396%   $94.5863   $94.59   $94.60   $94.60  
  Purchase #3 $6.86   6.734%   $7.322   $7.32   $7.30   $7.30  
  Purchase #4 $99.49   4.586%   $104.0526   $104.05   $104.05   $104.10  
  Purchase #5 $26.37   12.837%   $29.7551   $29.76   $29.75   $29.80  
  Purchase #6 $136.91   10.782%   $151.6716   $151.67   $151.65   $151.70  
  Purchase #7 $175.86   5.787%   $186.037   $186.04   $186.05   $186.00  
  7 purchase totals = $714.87       $764.1371   $764.14   $764.10   $764.20