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 $84.37   12.671%   $95.0605   $95.06   $95.05   $95.10  
  Purchase #2 $64.76   6.558%   $69.007   $69.01   $69.00   $69.00  
  Purchase #3 $36.55   3.316%   $37.762   $37.76   $37.75   $37.80  
  Purchase #4 $241.83   3.426%   $250.1151   $250.12   $250.10   $250.10  
  Purchase #5 $15.65   4.856%   $16.41   $16.41   $16.40   $16.40  
  Purchase #6 $30.45   3.321%   $31.4612   $31.46   $31.45   $31.50  
  Purchase #7 $30.98   3.309%   $32.0051   $32.01   $32.00   $32.00  
  7 purchase totals = $504.59       $531.8209   $531.83   $531.75   $531.90