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	$77.70	4.150%	$80.9246	$80.92	$80.90	$80.90
Purchase #2	$189.41	11.341%	$210.891	$210.89	$210.90	$210.90
Purchase #3	$194.85	12.258%	$218.7347	$218.73	$218.75	$218.70
Purchase #4	$141.48	13.508%	$160.5911	$160.59	$160.60	$160.60
Purchase #5	$6.56	10.208%	$7.2296	$7.23	$7.25	$7.20
Purchase #6	$114.92	13.667%	$130.6261	$130.63	$130.65	$130.60
Purchase #7	$62.51	13.699%	$71.0732	$71.07	$71.05	$71.10
7 purchase totals =	$787.43		$880.0703	$880.06	$880.10	$880.00