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 $161.65   12.587%   $181.9969   $182.00   $182.00   $182.00  
  Purchase #2 $25.88   4.295%   $26.9915   $26.99   $27.00   $27.00  
  Purchase #3 $209.64   10.495%   $231.6417   $231.64   $231.65   $231.60  
  Purchase #4 $103.77   12.374%   $116.6105   $116.61   $116.60   $116.60  
  Purchase #5 $190.70   8.175%   $206.2897   $206.29   $206.30   $206.30  
  Purchase #6 $185.26   13.693%   $210.6277   $210.63   $210.65   $210.60  
  Purchase #7 $115.35   10.548%   $127.5171   $127.52   $127.50   $127.50  
  7 purchase totals = $992.25       $1,101.6751   $1,101.68   $1,101.70   $1,101.60