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	$53.62	10.647%	$59.3289	$59.33	$59.35	$59.30
Purchase #2	$30.44	9.421%	$33.3078	$33.31	$33.30	$33.30
Purchase #3	$247.28	13.567%	$280.8285	$280.83	$280.85	$280.80
Purchase #4	$161.45	12.174%	$181.1049	$181.10	$181.10	$181.10
Purchase #5	$21.51	9.451%	$23.5429	$23.54	$23.55	$23.50
Purchase #6	$86.56	11.576%	$96.5802	$96.58	$96.60	$96.60
Purchase #7	$171.65	4.134%	$178.746	$178.75	$178.75	$178.70
7 purchase totals =	$772.51		$853.4392	$853.44	$853.50	$853.30