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	$36.25	12.860%	$40.9118	$40.91	$40.90	$40.90
Purchase #2	$31.41	12.586%	$35.3633	$35.36	$35.35	$35.40
Purchase #3	$105.69	13.367%	$119.8176	$119.82	$119.80	$119.80
Purchase #4	$9.93	12.640%	$11.1852	$11.19	$11.20	$11.20
Purchase #5	$164.71	13.832%	$187.4927	$187.49	$187.50	$187.50
Purchase #6	$32.44	3.563%	$33.5958	$33.60	$33.60	$33.60
Purchase #7	$134.33	7.403%	$144.2744	$144.27	$144.25	$144.30
7 purchase totals =	$514.76		$572.6408	$572.64	$572.60	$572.70