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	$63.92	11.562%	$71.3104	$71.31	$71.30	$71.30
Purchase #2	$201.34	13.848%	$229.2216	$229.22	$229.20	$229.20
Purchase #3	$131.69	10.114%	$145.0091	$145.01	$145.00	$145.00
Purchase #4	$103.82	11.733%	$116.0012	$116.00	$116.00	$116.00
Purchase #5	$204.34	10.226%	$225.2358	$225.24	$225.25	$225.20
Purchase #6	$73.52	12.746%	$82.8909	$82.89	$82.90	$82.90
Purchase #7	$144.44	5.305%	$152.1025	$152.10	$152.10	$152.10
7 purchase totals =	$923.07		$1,021.7715	$1,021.77	$1,021.75	$1,021.70