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	$218.25	12.868%	$246.3344	$246.33	$246.35	$246.30
Purchase #2	$113.32	10.479%	$125.1948	$125.19	$125.20	$125.20
Purchase #3	$79.90	11.465%	$89.0605	$89.06	$89.05	$89.10
Purchase #4	$5.54	6.422%	$5.8958	$5.90	$5.90	$5.90
Purchase #5	$108.88	13.283%	$123.3425	$123.34	$123.35	$123.30
Purchase #6	$92.96	11.335%	$103.497	$103.50	$103.50	$103.50
Purchase #7	$105.62	4.422%	$110.2905	$110.29	$110.30	$110.30
7 purchase totals =	$724.47		$803.6155	$803.61	$803.65	$803.60