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 $24.91   6.684%   $26.575   $26.58   $26.60   $26.60  
  Purchase #2 $60.86   6.570%   $64.8585   $64.86   $64.85   $64.90  
  Purchase #3 $171.63   9.154%   $187.341   $187.34   $187.35   $187.30  
  Purchase #4 $68.81   13.646%   $78.1998   $78.20   $78.20   $78.20  
  Purchase #5 $232.45   3.685%   $241.0158   $241.02   $241.00   $241.00  
  Purchase #6 $121.51   4.665%   $127.1784   $127.18   $127.20   $127.20  
  Purchase #7 $188.51   6.382%   $200.5407   $200.54   $200.55   $200.50  
  7 purchase totals = $868.68       $925.7092   $925.72   $925.75   $925.70