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	$94.65	6.212%	$100.5297	$100.53	$100.55	$100.50
Purchase #2	$130.76	5.487%	$137.9348	$137.93	$137.95	$137.90
Purchase #3	$82.56	7.811%	$89.0088	$89.01	$89.00	$89.00
Purchase #4	$185.76	11.754%	$207.5942	$207.59	$207.60	$207.60
Purchase #5	$210.67	12.234%	$236.4434	$236.44	$236.45	$236.40
Purchase #6	$246.72	11.274%	$274.5352	$274.54	$274.55	$274.50
Purchase #7	$233.83	3.764%	$242.6314	$242.63	$242.65	$242.60
7 purchase totals =	$1,184.95		$1,288.6775	$1,288.67	$1,288.75	$1,288.50