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	$180.42	3.850%	$187.3662	$187.37	$187.35	$187.40
Purchase #2	$202.66	9.568%	$222.0505	$222.05	$222.05	$222.10
Purchase #3	$179.80	10.528%	$198.7293	$198.73	$198.75	$198.70
Purchase #4	$142.89	7.345%	$153.3853	$153.39	$153.40	$153.40
Purchase #5	$39.31	11.516%	$43.8369	$43.84	$43.85	$43.80
Purchase #6	$134.73	7.152%	$144.3659	$144.37	$144.35	$144.40
Purchase #7	$18.80	10.659%	$20.8039	$20.80	$20.80	$20.80
7 purchase totals =	$898.61		$970.5380	$970.55	$970.55	$970.60