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	$176.72	13.359%	$200.328	$200.33	$200.35	$200.30
Purchase #2	$125.75	9.558%	$137.7692	$137.77	$137.75	$137.80
Purchase #3	$250.78	3.244%	$258.9153	$258.92	$258.90	$258.90
Purchase #4	$133.33	11.696%	$148.9243	$148.92	$148.90	$148.90
Purchase #5	$173.40	9.474%	$189.8279	$189.83	$189.85	$189.80
Purchase #6	$136.33	9.458%	$149.2241	$149.22	$149.20	$149.20
Purchase #7	$61.83	9.503%	$67.7057	$67.71	$67.70	$67.70
7 purchase totals =	$1,058.14		$1,152.6945	$1,152.70	$1,152.65	$1,152.60