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 $26.25   11.255%   $29.2044   $29.20   $29.20   $29.20  
  Purchase #2 $139.98   10.126%   $154.1544   $154.15   $154.15   $154.20  
  Purchase #3 $250.69   8.805%   $272.7633   $272.76   $272.75   $272.80  
  Purchase #4 $83.44   8.667%   $90.6717   $90.67   $90.65   $90.70  
  Purchase #5 $33.47   10.493%   $36.982   $36.98   $37.00   $37.00  
  Purchase #6 $92.37   9.730%   $101.3576   $101.36   $101.35   $101.40  
  Purchase #7 $228.69   5.726%   $241.7848   $241.78   $241.80   $241.80  
  7 purchase totals = $854.89       $926.9182   $926.90   $926.90   $927.10