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	$25.85	5.501%	$27.272	$27.27	$27.25	$27.30
Purchase #2	$50.75	4.524%	$53.0459	$53.05	$53.05	$53.00
Purchase #3	$127.92	11.689%	$142.8726	$142.87	$142.85	$142.90
Purchase #4	$234.82	4.307%	$244.9337	$244.93	$244.95	$244.90
Purchase #5	$183.89	4.495%	$192.1559	$192.16	$192.15	$192.20
Purchase #6	$186.38	7.410%	$200.1908	$200.19	$200.20	$200.20
Purchase #7	$160.87	11.659%	$179.6258	$179.63	$179.65	$179.60
7 purchase totals =	$970.48		$1,040.0967	$1,040.10	$1,040.10	$1,040.10