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	$71.63	12.802%	$80.8001	$80.80	$80.80	$80.80
Purchase #2	$158.37	13.817%	$180.252	$180.25	$180.25	$180.30
Purchase #3	$131.94	11.729%	$147.4152	$147.42	$147.40	$147.40
Purchase #4	$237.84	7.318%	$255.2451	$255.25	$255.25	$255.20
Purchase #5	$79.56	3.283%	$82.172	$82.17	$82.15	$82.20
Purchase #6	$19.30	5.485%	$20.3586	$20.36	$20.35	$20.40
Purchase #7	$235.70	10.343%	$260.0785	$260.08	$260.10	$260.10
7 purchase totals =	$934.34		$1,026.3215	$1,026.33	$1,026.30	$1,026.40