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	$138.75	6.330%	$147.5329	$147.53	$147.55	$147.50
Purchase #2	$96.80	3.455%	$100.1444	$100.14	$100.15	$100.10
Purchase #3	$47.65	13.490%	$54.078	$54.08	$54.10	$54.10
Purchase #4	$41.27	6.760%	$44.0599	$44.06	$44.05	$44.10
Purchase #5	$90.35	10.790%	$100.0988	$100.10	$100.10	$100.10
Purchase #6	$74.81	10.626%	$82.7593	$82.76	$82.75	$82.80
Purchase #7	$119.28	9.354%	$130.4375	$130.44	$130.45	$130.40
7 purchase totals =	$608.91		$659.1108	$659.11	$659.15	$659.10