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 $69.55   5.866%   $73.6298   $73.63   $73.65   $73.60  
  Purchase #2 $247.61   6.555%   $263.8408   $263.84   $263.85   $263.80  
  Purchase #3 $188.71   6.797%   $201.5366   $201.54   $201.55   $201.50  
  Purchase #4 $116.33   12.492%   $130.8619   $130.86   $130.85   $130.90  
  Purchase #5 $144.74   13.793%   $164.704   $164.70   $164.70   $164.70  
  Purchase #6 $137.40   4.177%   $143.1392   $143.14   $143.15   $143.10  
  Purchase #7 $74.63   5.594%   $78.8048   $78.80   $78.80   $78.80  
  7 purchase totals = $978.97       $1,056.5171   $1,056.51   $1,056.55   $1,056.40