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	$40.72	3.180%	$42.0149	$42.01	$42.00	$42.00
Purchase #2	$210.34	3.125%	$216.9131	$216.91	$216.90	$216.90
Purchase #3	$171.34	13.687%	$194.7913	$194.79	$194.80	$194.80
Purchase #4	$12.94	10.455%	$14.2929	$14.29	$14.30	$14.30
Purchase #5	$101.50	10.334%	$111.989	$111.99	$112.00	$112.00
Purchase #6	$28.81	12.681%	$32.4634	$32.46	$32.45	$32.50
Purchase #7	$168.77	7.214%	$180.9451	$180.95	$180.95	$180.90
7 purchase totals =	$734.42		$793.4097	$793.40	$793.40	$793.40