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	$122.64	13.711%	$139.4552	$139.46	$139.45	$139.50
Purchase #2	$25.36	7.798%	$27.3376	$27.34	$27.35	$27.30
Purchase #3	$22.51	12.187%	$25.2533	$25.25	$25.25	$25.30
Purchase #4	$146.28	11.241%	$162.7233	$162.72	$162.70	$162.70
Purchase #5	$131.43	4.825%	$137.7715	$137.77	$137.75	$137.80
Purchase #6	$239.87	4.427%	$250.489	$250.49	$250.50	$250.50
Purchase #7	$219.54	8.605%	$238.4314	$238.43	$238.45	$238.40
7 purchase totals =	$907.63		$981.4613	$981.46	$981.45	$981.50