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 $72.83   3.766%   $75.5728   $75.57   $75.55   $75.60  
  Purchase #2 $107.92   11.141%   $119.9434   $119.94   $119.95   $119.90  
  Purchase #3 $179.71   4.104%   $187.0853   $187.09   $187.10   $187.10  
  Purchase #4 $179.61   10.511%   $198.4888   $198.49   $198.50   $198.50  
  Purchase #5 $173.29   5.310%   $182.4917   $182.49   $182.50   $182.50  
  Purchase #6 $57.27   6.173%   $60.8053   $60.81   $60.80   $60.80  
  Purchase #7 $209.64   6.661%   $223.6041   $223.60   $223.60   $223.60  
  7 purchase totals = $980.27       $1,047.9914   $1,047.99   $1,048.00   $1,048.00