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	$118.95	3.827%	$123.5022	$123.50	$123.50	$123.50
Purchase #2	$230.52	8.251%	$249.5402	$249.54	$249.55	$249.50
Purchase #3	$181.30	3.497%	$187.6401	$187.64	$187.65	$187.60
Purchase #4	$102.36	12.793%	$115.4549	$115.45	$115.45	$115.50
Purchase #5	$202.47	10.373%	$223.4722	$223.47	$223.45	$223.50
Purchase #6	$233.40	13.333%	$264.5192	$264.52	$264.50	$264.50
Purchase #7	$158.72	13.296%	$179.8234	$179.82	$179.80	$179.80
7 purchase totals =	$1,227.72		$1,343.9522	$1,343.94	$1,343.90	$1,343.90