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 $119.98   4.547%   $125.4355   $125.44   $125.45   $125.40  
  Purchase #2 $80.69   13.350%   $91.4621   $91.46   $91.45   $91.50  
  Purchase #3 $51.54   6.258%   $54.7654   $54.77   $54.75   $54.80  
  Purchase #4 $250.25   11.228%   $278.3481   $278.35   $278.35   $278.30  
  Purchase #5 $239.28   12.197%   $268.465   $268.47   $268.45   $268.50  
  Purchase #6 $196.55   11.745%   $219.6348   $219.63   $219.65   $219.60  
  Purchase #7 $176.69   13.740%   $200.9672   $200.97   $200.95   $201.00  
  7 purchase totals = $1,114.98       $1,239.0781   $1,239.09   $1,239.05   $1,239.10