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 $210.80   13.117%   $238.4506   $238.45   $238.45   $238.50  
  Purchase #2 $249.85   12.760%   $281.7309   $281.73   $281.75   $281.70  
  Purchase #3 $212.36   12.741%   $239.4168   $239.42   $239.40   $239.40  
  Purchase #4 $231.92   4.176%   $241.605   $241.61   $241.60   $241.60  
  Purchase #5 $220.97   8.455%   $239.653   $239.65   $239.65   $239.70  
  Purchase #6 $64.50   6.267%   $68.5422   $68.54   $68.55   $68.50  
  Purchase #7 $86.29   5.196%   $90.7736   $90.77   $90.75   $90.80  
  7 purchase totals = $1,276.69       $1,400.1721   $1,400.17   $1,400.15   $1,400.20