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 $146.80   10.368%   $162.0202   $162.02   $162.00   $162.00  
  Purchase #2 $179.63   6.250%   $190.8569   $190.86   $190.85   $190.90  
  Purchase #3 $222.92   6.479%   $237.363   $237.36   $237.35   $237.40  
  Purchase #4 $158.85   11.827%   $177.6372   $177.64   $177.65   $177.60  
  Purchase #5 $106.83   8.730%   $116.1563   $116.16   $116.15   $116.20  
  Purchase #6 $149.67   10.594%   $165.526   $165.53   $165.55   $165.50  
  Purchase #7 $7.54   9.221%   $8.2353   $8.24   $8.25   $8.20  
  7 purchase totals = $972.24       $1,057.7949   $1,057.81   $1,057.80   $1,057.80