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	$26.62	8.421%	$28.8617	$28.86	$28.85	$28.90
Purchase #2	$249.42	9.510%	$273.1398	$273.14	$273.15	$273.10
Purchase #3	$136.95	10.751%	$151.6735	$151.67	$151.65	$151.70
Purchase #4	$29.37	9.712%	$32.2224	$32.22	$32.20	$32.20
Purchase #5	$119.42	4.184%	$124.4165	$124.42	$124.40	$124.40
Purchase #6	$11.76	12.801%	$13.2654	$13.27	$13.25	$13.30
Purchase #7	$174.63	12.388%	$196.2632	$196.26	$196.25	$196.30
7 purchase totals =	$748.17		$819.8425	$819.84	$819.75	$819.90