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 $236.51   5.116%   $248.6099   $248.61   $248.60   $248.60  
  Purchase #2 $239.30   9.752%   $262.6365   $262.64   $262.65   $262.60  
  Purchase #3 $176.75   13.163%   $200.0156   $200.02   $200.00   $200.00  
  Purchase #4 $239.70   7.254%   $257.0878   $257.09   $257.10   $257.10  
  Purchase #5 $30.56   4.761%   $32.015   $32.02   $32.00   $32.00  
  Purchase #6 $198.91   6.790%   $212.416   $212.42   $212.40   $212.40  
  Purchase #7 $196.73   3.745%   $204.0975   $204.10   $204.10   $204.10  
  7 purchase totals = $1,318.46       $1,416.8783   $1,416.90   $1,416.85   $1,416.80