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	$8.81	7.723%	$9.4904	$9.49	$9.50	$9.50
Purchase #2	$170.62	5.807%	$180.5279	$180.53	$180.55	$180.50
Purchase #3	$114.39	11.793%	$127.88	$127.88	$127.90	$127.90
Purchase #4	$58.49	12.236%	$65.6468	$65.65	$65.65	$65.60
Purchase #5	$39.90	4.102%	$41.5367	$41.54	$41.55	$41.50
Purchase #6	$111.53	11.728%	$124.6102	$124.61	$124.60	$124.60
Purchase #7	$82.54	7.530%	$88.7553	$88.76	$88.75	$88.80
7 purchase totals =	$586.28		$638.4473	$638.46	$638.50	$638.40