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 $227.62   11.486%   $253.7644   $253.76   $253.75   $253.80  
  Purchase #2 $186.73   7.346%   $200.4472   $200.45   $200.45   $200.40  
  Purchase #3 $187.90   4.769%   $196.861   $196.86   $196.85   $196.90  
  Purchase #4 $160.46   13.403%   $181.9665   $181.97   $181.95   $182.00  
  Purchase #5 $82.50   13.106%   $93.3125   $93.31   $93.30   $93.30  
  Purchase #6 $65.29   8.619%   $70.9173   $70.92   $70.90   $70.90  
  Purchase #7 $207.41   12.807%   $233.973   $233.97   $233.95   $234.00  
  7 purchase totals = $1,117.91       $1,231.2419   $1,231.24   $1,231.15   $1,231.30