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	$74.62	5.185%	$78.489	$78.49	$78.50	$78.50
Purchase #2	$37.44	9.668%	$41.0597	$41.06	$41.05	$41.10
Purchase #3	$56.97	11.140%	$63.3165	$63.32	$63.30	$63.30
Purchase #4	$52.96	9.731%	$58.1135	$58.11	$58.10	$58.10
Purchase #5	$17.60	6.582%	$18.7584	$18.76	$18.75	$18.80
Purchase #6	$210.94	5.637%	$222.8307	$222.83	$222.85	$222.80
Purchase #7	$56.28	5.104%	$59.1525	$59.15	$59.15	$59.20
7 purchase totals =	$506.81		$541.7203	$541.72	$541.70	$541.80