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 $161.89   13.761%   $184.1677   $184.17   $184.15   $184.20  
  Purchase #2 $66.69   8.841%   $72.5861   $72.59   $72.60   $72.60  
  Purchase #3 $216.87   3.160%   $223.7231   $223.72   $223.70   $223.70  
  Purchase #4 $116.49   3.394%   $120.4437   $120.44   $120.45   $120.40  
  Purchase #5 $187.99   3.682%   $194.9118   $194.91   $194.90   $194.90  
  Purchase #6 $180.71   11.125%   $200.814   $200.81   $200.80   $200.80  
  Purchase #7 $193.90   10.454%   $214.1703   $214.17   $214.15   $214.20  
  7 purchase totals = $1,124.54       $1,210.8167   $1,210.81   $1,210.75   $1,210.80