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 $63.76   3.249%   $65.8316   $65.83   $65.85   $65.80  
  Purchase #2 $105.95   13.790%   $120.5605   $120.56   $120.55   $120.60  
  Purchase #3 $120.73   12.216%   $135.4784   $135.48   $135.50   $135.50  
  Purchase #4 $125.89   10.537%   $139.155   $139.16   $139.15   $139.20  
  Purchase #5 $241.97   4.107%   $251.9077   $251.91   $251.90   $251.90  
  Purchase #6 $165.93   4.768%   $173.8415   $173.84   $173.85   $173.80  
  Purchase #7 $199.59   12.859%   $225.2553   $225.26   $225.25   $225.30  
  7 purchase totals = $1,023.82       $1,112.0300   $1,112.04   $1,112.05   $1,112.10