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	$28.90	10.615%	$31.9677	$31.97	$31.95	$32.00
Purchase #2	$124.27	9.476%	$136.0458	$136.05	$136.05	$136.00
Purchase #3	$133.56	6.620%	$142.4017	$142.40	$142.40	$142.40
Purchase #4	$43.35	5.356%	$45.6718	$45.67	$45.65	$45.70
Purchase #5	$223.31	13.229%	$252.8517	$252.85	$252.85	$252.90
Purchase #6	$226.66	10.667%	$250.8378	$250.84	$250.85	$250.80
Purchase #7	$169.89	6.201%	$180.4249	$180.42	$180.40	$180.40
7 purchase totals =	$949.94		$1,040.2014	$1,040.20	$1,040.15	$1,040.20