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	$249.88	9.741%	$274.2208	$274.22	$274.20	$274.20
Purchase #2	$111.69	9.122%	$121.8784	$121.88	$121.90	$121.90
Purchase #3	$90.90	11.396%	$101.259	$101.26	$101.25	$101.30
Purchase #4	$214.49	3.558%	$222.1216	$222.12	$222.10	$222.10
Purchase #5	$46.28	6.556%	$49.3141	$49.31	$49.30	$49.30
Purchase #6	$75.31	11.473%	$83.9503	$83.95	$83.95	$84.00
Purchase #7	$112.59	13.474%	$127.7604	$127.76	$127.75	$127.80
7 purchase totals =	$901.14		$980.5046	$980.50	$980.45	$980.60