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 $118.44   12.423%   $133.1538   $133.15   $133.15   $133.20  
  Purchase #2 $56.86   4.588%   $59.4687   $59.47   $59.45   $59.50  
  Purchase #3 $32.81   6.609%   $34.9784   $34.98   $35.00   $35.00  
  Purchase #4 $154.73   5.382%   $163.0576   $163.06   $163.05   $163.10  
  Purchase #5 $147.88   13.259%   $167.4874   $167.49   $167.50   $167.50  
  Purchase #6 $248.73   13.558%   $282.4528   $282.45   $282.45   $282.50  
  Purchase #7 $194.89   9.130%   $212.6835   $212.68   $212.70   $212.70  
  7 purchase totals = $954.34       $1,053.2822   $1,053.28   $1,053.30   $1,053.50