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	$108.73	8.606%	$118.0873	$118.09	$118.10	$118.10
Purchase #2	$67.58	3.850%	$70.1818	$70.18	$70.20	$70.20
Purchase #3	$238.71	4.594%	$249.6763	$249.68	$249.70	$249.70
Purchase #4	$240.42	8.169%	$260.0599	$260.06	$260.05	$260.10
Purchase #5	$78.47	12.463%	$88.2497	$88.25	$88.25	$88.20
Purchase #6	$92.56	11.588%	$103.2859	$103.29	$103.30	$103.30
Purchase #7	$187.31	12.528%	$210.7762	$210.78	$210.80	$210.80
7 purchase totals =	$1,013.78		$1,100.3171	$1,100.33	$1,100.40	$1,100.40