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	$49.43	11.361%	$55.0457	$55.05	$55.05	$55.00
Purchase #2	$35.88	8.556%	$38.9499	$38.95	$38.95	$38.90
Purchase #3	$143.25	5.398%	$150.9826	$150.98	$151.00	$151.00
Purchase #4	$231.30	13.781%	$263.1755	$263.18	$263.20	$263.20
Purchase #5	$43.57	4.475%	$45.5198	$45.52	$45.50	$45.50
Purchase #6	$179.89	13.851%	$204.8066	$204.81	$204.80	$204.80
Purchase #7	$172.46	5.203%	$181.4331	$181.43	$181.45	$181.40
7 purchase totals =	$855.78		$939.9132	$939.92	$939.95	$939.80