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 $23.57   10.320%   $26.0024   $26.00   $26.00   $26.00  
  Purchase #2 $96.58   6.411%   $102.7717   $102.77   $102.75   $102.80  
  Purchase #3 $33.60   9.480%   $36.7853   $36.79   $36.80   $36.80  
  Purchase #4 $236.77   10.770%   $262.2701   $262.27   $262.25   $262.30  
  Purchase #5 $40.79   13.812%   $46.4239   $46.42   $46.40   $46.40  
  Purchase #6 $238.69   5.235%   $251.1854   $251.19   $251.20   $251.20  
  Purchase #7 $23.37   3.748%   $24.2459   $24.25   $24.25   $24.20  
  7 purchase totals = $693.37       $749.6847   $749.69   $749.65   $749.70