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	$200.50	11.349%	$223.2547	$223.25	$223.25	$223.30
Purchase #2	$182.51	6.327%	$194.0574	$194.06	$194.05	$194.10
Purchase #3	$237.63	12.829%	$268.1156	$268.12	$268.10	$268.10
Purchase #4	$197.72	10.800%	$219.0738	$219.07	$219.05	$219.10
Purchase #5	$219.77	11.127%	$244.2238	$244.22	$244.20	$244.20
Purchase #6	$21.36	3.351%	$22.0758	$22.08	$22.10	$22.10
Purchase #7	$105.76	3.557%	$109.5219	$109.52	$109.50	$109.50
7 purchase totals =	$1,165.25		$1,280.3230	$1,280.32	$1,280.25	$1,280.40