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	$51.64	6.200%	$54.8417	$54.84	$54.85	$54.80
Purchase #2	$243.26	4.851%	$255.0605	$255.06	$255.05	$255.10
Purchase #3	$103.79	7.298%	$111.3646	$111.36	$111.35	$111.40
Purchase #4	$187.66	6.235%	$199.3606	$199.36	$199.35	$199.40
Purchase #5	$142.78	5.179%	$150.1746	$150.17	$150.15	$150.20
Purchase #6	$229.56	9.264%	$250.8264	$250.83	$250.85	$250.80
Purchase #7	$231.58	6.820%	$247.3738	$247.37	$247.35	$247.40
7 purchase totals =	$1,190.27		$1,269.0022	$1,268.99	$1,268.95	$1,269.10