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	$75.52	5.346%	$79.5573	$79.56	$79.55	$79.60
Purchase #2	$203.31	11.563%	$226.8187	$226.82	$226.80	$226.80
Purchase #3	$39.42	7.830%	$42.5066	$42.51	$42.50	$42.50
Purchase #4	$131.28	12.327%	$147.4629	$147.46	$147.45	$147.50
Purchase #5	$243.82	4.757%	$255.4185	$255.42	$255.40	$255.40
Purchase #6	$233.39	6.379%	$248.2779	$248.28	$248.30	$248.30
Purchase #7	$54.92	7.140%	$58.8413	$58.84	$58.85	$58.80
7 purchase totals =	$981.66		$1,058.8832	$1,058.89	$1,058.85	$1,058.90