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 $24.64   5.557%   $26.0092   $26.01   $26.00   $26.00  
  Purchase #2 $147.65   6.784%   $157.6666   $157.67   $157.65   $157.70  
  Purchase #3 $232.49   3.500%   $240.6272   $240.63   $240.65   $240.60  
  Purchase #4 $125.95   3.495%   $130.352   $130.35   $130.35   $130.40  
  Purchase #5 $74.28   12.861%   $83.8332   $83.83   $83.85   $83.80  
  Purchase #6 $76.42   5.377%   $80.5291   $80.53   $80.55   $80.50  
  Purchase #7 $125.56   3.854%   $130.3991   $130.40   $130.40   $130.40  
  7 purchase totals = $806.99       $849.4164   $849.42   $849.45   $849.40