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 $120.29   4.197%   $125.3386   $125.34   $125.35   $125.30  
  Purchase #2 $12.91   13.298%   $14.6268   $14.63   $14.65   $14.60  
  Purchase #3 $220.98   4.214%   $230.2921   $230.29   $230.30   $230.30  
  Purchase #4 $61.93   12.816%   $69.8669   $69.87   $69.85   $69.90  
  Purchase #5 $35.65   3.731%   $36.9801   $36.98   $37.00   $37.00  
  Purchase #6 $114.76   8.838%   $124.9025   $124.90   $124.90   $124.90  
  Purchase #7 $176.84   3.628%   $183.2558   $183.26   $183.25   $183.30  
  7 purchase totals = $743.36       $785.2628   $785.27   $785.30   $785.30