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 $207.52   13.802%   $236.1619   $236.16   $236.15   $236.20  
  Purchase #2 $219.93   5.184%   $231.3312   $231.33   $231.35   $231.30  
  Purchase #3 $249.77   3.245%   $257.875   $257.88   $257.90   $257.90  
  Purchase #4 $106.69   5.577%   $112.6401   $112.64   $112.65   $112.60  
  Purchase #5 $111.48   13.865%   $126.9367   $126.94   $126.95   $126.90  
  Purchase #6 $159.44   13.783%   $181.4156   $181.42   $181.40   $181.40  
  Purchase #7 $141.86   6.787%   $151.488   $151.49   $151.50   $151.50  
  7 purchase totals = $1,196.69       $1,297.8485   $1,297.86   $1,297.90   $1,297.80