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	$180.40	11.111%	$200.4442	$200.44	$200.45	$200.40
Purchase #2	$36.99	12.221%	$41.5105	$41.51	$41.50	$41.50
Purchase #3	$52.57	13.244%	$59.5324	$59.53	$59.55	$59.50
Purchase #4	$48.39	4.860%	$50.7418	$50.74	$50.75	$50.70
Purchase #5	$31.84	6.108%	$33.7848	$33.78	$33.80	$33.80
Purchase #6	$78.88	3.405%	$81.5659	$81.57	$81.55	$81.60
Purchase #7	$104.79	10.443%	$115.7332	$115.73	$115.75	$115.70
7 purchase totals =	$533.86		$583.3128	$583.30	$583.35	$583.20