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	$198.78	13.434%	$225.4841	$225.48	$225.50	$225.50
Purchase #2	$189.86	3.600%	$196.695	$196.70	$196.70	$196.70
Purchase #3	$173.54	3.353%	$179.3588	$179.36	$179.35	$179.40
Purchase #4	$221.59	3.209%	$228.7008	$228.70	$228.70	$228.70
Purchase #5	$65.28	13.255%	$73.9329	$73.93	$73.95	$73.90
Purchase #6	$55.93	3.375%	$57.8176	$57.82	$57.80	$57.80
Purchase #7	$134.52	3.264%	$138.9107	$138.91	$138.90	$138.90
7 purchase totals =	$1,039.50		$1,100.8999	$1,100.90	$1,100.90	$1,100.90