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	$203.25	6.206%	$215.8637	$215.86	$215.85	$215.90
Purchase #2	$236.46	13.733%	$268.9331	$268.93	$268.95	$268.90
Purchase #3	$247.43	5.636%	$261.3752	$261.38	$261.40	$261.40
Purchase #4	$90.78	9.762%	$99.6419	$99.64	$99.65	$99.60
Purchase #5	$45.78	10.753%	$50.7027	$50.70	$50.70	$50.70
Purchase #6	$233.48	12.647%	$263.0082	$263.01	$263.00	$263.00
Purchase #7	$147.90	3.257%	$152.7171	$152.72	$152.70	$152.70
7 purchase totals =	$1,205.08		$1,312.2419	$1,312.24	$1,312.25	$1,312.20