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	$243.48	13.194%	$275.6048	$275.60	$275.60	$275.60
Purchase #2	$224.31	12.224%	$251.7297	$251.73	$251.75	$251.70
Purchase #3	$85.72	5.564%	$90.4895	$90.49	$90.50	$90.50
Purchase #4	$134.82	3.688%	$139.7922	$139.79	$139.80	$139.80
Purchase #5	$47.41	5.361%	$49.9517	$49.95	$49.95	$50.00
Purchase #6	$34.88	4.415%	$36.42	$36.42	$36.40	$36.40
Purchase #7	$80.89	12.595%	$91.0781	$91.08	$91.10	$91.10
7 purchase totals =	$851.51		$935.0660	$935.06	$935.10	$935.10