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 $66.66   3.488%   $68.9851   $68.99   $69.00   $69.00  
  Purchase #2 $237.80   8.197%   $257.2925   $257.29   $257.30   $257.30  
  Purchase #3 $187.28   3.403%   $193.6531   $193.65   $193.65   $193.70  
  Purchase #4 $99.31   5.358%   $104.631   $104.63   $104.65   $104.60  
  Purchase #5 $108.92   7.153%   $116.711   $116.71   $116.70   $116.70  
  Purchase #6 $224.91   8.395%   $243.7912   $243.79   $243.80   $243.80  
  Purchase #7 $213.29   9.615%   $233.7978   $233.80   $233.80   $233.80  
  7 purchase totals = $1,138.17       $1,218.8617   $1,218.86   $1,218.90   $1,218.90