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	$48.49	11.851%	$54.2365	$54.24	$54.25	$54.20
Purchase #2	$85.55	6.261%	$90.9063	$90.91	$90.90	$90.90
Purchase #3	$189.53	10.825%	$210.0466	$210.05	$210.05	$210.00
Purchase #4	$80.77	11.274%	$89.876	$89.88	$89.90	$89.90
Purchase #5	$248.63	9.613%	$272.5308	$272.53	$272.55	$272.50
Purchase #6	$247.79	12.115%	$277.8098	$277.81	$277.80	$277.80
Purchase #7	$32.99	7.122%	$35.3395	$35.34	$35.35	$35.30
7 purchase totals =	$933.75		$1,030.7455	$1,030.76	$1,030.80	$1,030.60