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 $63.53   5.176%   $66.8183   $66.82   $66.80   $66.80  
  Purchase #2 $182.59   7.546%   $196.3682   $196.37   $196.35   $196.40  
  Purchase #3 $23.96   4.459%   $25.0284   $25.03   $25.05   $25.00  
  Purchase #4 $217.33   6.661%   $231.8064   $231.81   $231.80   $231.80  
  Purchase #5 $171.95   11.262%   $191.315   $191.32   $191.30   $191.30  
  Purchase #6 $222.68   12.653%   $250.8557   $250.86   $250.85   $250.90  
  Purchase #7 $223.63   3.751%   $232.0184   $232.02   $232.00   $232.00  
  7 purchase totals = $1,105.67       $1,194.2104   $1,194.23   $1,194.15   $1,194.20