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	$184.91	5.341%	$194.786	$194.79	$194.80	$194.80
Purchase #2	$143.89	4.450%	$150.2931	$150.29	$150.30	$150.30
Purchase #3	$169.31	3.391%	$175.0513	$175.05	$175.05	$175.10
Purchase #4	$210.68	5.114%	$221.4542	$221.45	$221.45	$221.50
Purchase #5	$223.90	9.109%	$244.2951	$244.30	$244.30	$244.30
Purchase #6	$72.69	12.298%	$81.6294	$81.63	$81.65	$81.60
Purchase #7	$217.46	7.280%	$233.2911	$233.29	$233.30	$233.30
7 purchase totals =	$1,222.84		$1,300.8002	$1,300.80	$1,300.85	$1,300.90