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	$20.28	10.854%	$22.4812	$22.48	$22.50	$22.50
Purchase #2	$55.92	12.323%	$62.811	$62.81	$62.80	$62.80
Purchase #3	$219.73	11.613%	$245.2472	$245.25	$245.25	$245.20
Purchase #4	$201.96	10.661%	$223.491	$223.49	$223.50	$223.50
Purchase #5	$110.76	7.235%	$118.7735	$118.77	$118.75	$118.80
Purchase #6	$226.32	3.367%	$233.9402	$233.94	$233.95	$233.90
Purchase #7	$243.45	13.255%	$275.7193	$275.72	$275.70	$275.70
7 purchase totals =	$1,078.42		$1,182.4634	$1,182.46	$1,182.45	$1,182.40