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	$87.46	13.388%	$99.1691	$99.17	$99.15	$99.20
Purchase #2	$189.89	13.142%	$214.8453	$214.85	$214.85	$214.80
Purchase #3	$237.83	5.477%	$250.8559	$250.86	$250.85	$250.90
Purchase #4	$213.61	5.480%	$225.3158	$225.32	$225.30	$225.30
Purchase #5	$86.99	7.234%	$93.2829	$93.28	$93.30	$93.30
Purchase #6	$20.72	10.717%	$22.9406	$22.94	$22.95	$22.90
Purchase #7	$153.82	13.196%	$174.1181	$174.12	$174.10	$174.10
7 purchase totals =	$990.32		$1,080.5277	$1,080.54	$1,080.50	$1,080.50