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 $247.42   10.154%   $272.543   $272.54   $272.55   $272.50  
  Purchase #2 $113.82   5.283%   $119.8331   $119.83   $119.85   $119.80  
  Purchase #3 $77.77   8.309%   $84.2319   $84.23   $84.25   $84.20  
  Purchase #4 $184.93   7.722%   $199.2103   $199.21   $199.20   $199.20  
  Purchase #5 $208.28   8.588%   $226.1671   $226.17   $226.15   $226.20  
  Purchase #6 $207.90   13.514%   $235.9956   $236.00   $236.00   $236.00  
  Purchase #7 $30.41   11.677%   $33.961   $33.96   $33.95   $34.00  
  7 purchase totals = $1,070.53       $1,171.9420   $1,171.94   $1,171.95   $1,171.90