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	$90.85	11.682%	$101.4631	$101.46	$101.45	$101.50
Purchase #2	$233.43	13.394%	$264.6956	$264.70	$264.70	$264.70
Purchase #3	$131.73	6.188%	$139.8815	$139.88	$139.90	$139.90
Purchase #4	$248.99	12.400%	$279.8648	$279.86	$279.85	$279.90
Purchase #5	$105.60	3.851%	$109.6667	$109.67	$109.65	$109.70
Purchase #6	$124.51	4.715%	$130.3806	$130.38	$130.40	$130.40
Purchase #7	$68.63	9.219%	$74.957	$74.96	$74.95	$75.00
7 purchase totals =	$1,003.74		$1,100.9093	$1,100.91	$1,100.90	$1,101.10