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	$38.71	8.217%	$41.8908	$41.89	$41.90	$41.90
Purchase #2	$71.49	10.645%	$79.1001	$79.10	$79.10	$79.10
Purchase #3	$215.72	5.819%	$228.2727	$228.27	$228.25	$228.30
Purchase #4	$40.76	12.479%	$45.8464	$45.85	$45.85	$45.80
Purchase #5	$218.52	7.656%	$235.2499	$235.25	$235.25	$235.20
Purchase #6	$131.60	11.486%	$146.7156	$146.72	$146.70	$146.70
Purchase #7	$207.40	7.128%	$222.1835	$222.18	$222.20	$222.20
7 purchase totals =	$924.20		$999.2590	$999.26	$999.25	$999.20