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 $56.47   9.296%   $61.7195   $61.72   $61.70   $61.70  
  Purchase #2 $116.54   8.267%   $126.1744   $126.17   $126.15   $126.20  
  Purchase #3 $207.82   8.416%   $225.3101   $225.31   $225.30   $225.30  
  Purchase #4 $180.75   3.586%   $187.2317   $187.23   $187.25   $187.20  
  Purchase #5 $227.70   7.695%   $245.2215   $245.22   $245.20   $245.20  
  Purchase #6 $193.45   10.827%   $214.3948   $214.39   $214.40   $214.40  
  Purchase #7 $61.46   5.524%   $64.8551   $64.86   $64.85   $64.90  
  7 purchase totals = $1,044.19       $1,124.9071   $1,124.90   $1,124.85   $1,124.90