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	$72.71	13.816%	$82.7556	$82.76	$82.75	$82.80
Purchase #2	$6.33	10.450%	$6.9915	$6.99	$7.00	$7.00
Purchase #3	$237.48	12.388%	$266.899	$266.90	$266.90	$266.90
Purchase #4	$202.80	9.244%	$221.5468	$221.55	$221.55	$221.50
Purchase #5	$82.89	10.169%	$91.3191	$91.32	$91.30	$91.30
Purchase #6	$67.35	6.140%	$71.4853	$71.49	$71.50	$71.50
Purchase #7	$176.59	3.713%	$183.1468	$183.15	$183.15	$183.10
7 purchase totals =	$846.15		$924.1441	$924.16	$924.15	$924.10