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 $108.95   9.524%   $119.3264   $119.33   $119.35   $119.30  
  Purchase #2 $213.57   8.467%   $231.653   $231.65   $231.65   $231.70  
  Purchase #3 $64.50   3.812%   $66.9587   $66.96   $66.95   $67.00  
  Purchase #4 $34.39   12.429%   $38.6643   $38.66   $38.65   $38.70  
  Purchase #5 $117.86   13.690%   $133.995   $134.00   $134.00   $134.00  
  Purchase #6 $34.31   3.463%   $35.4982   $35.50   $35.50   $35.50  
  Purchase #7 $133.75   4.443%   $139.6925   $139.69   $139.70   $139.70  
  7 purchase totals = $707.33       $765.7881   $765.79   $765.80   $765.90