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	$79.63	12.123%	$89.2835	$89.28	$89.30	$89.30
Purchase #2	$130.90	9.204%	$142.948	$142.95	$142.95	$142.90
Purchase #3	$218.75	11.545%	$244.0047	$244.00	$244.00	$244.00
Purchase #4	$190.46	4.428%	$198.8936	$198.89	$198.90	$198.90
Purchase #5	$248.75	7.792%	$268.1326	$268.13	$268.15	$268.10
Purchase #6	$131.30	8.294%	$142.19	$142.19	$142.20	$142.20
Purchase #7	$178.98	9.551%	$196.0744	$196.07	$196.05	$196.10
7 purchase totals =	$1,178.77		$1,281.5268	$1,281.51	$1,281.55	$1,281.50