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	$9.51	13.751%	$10.8177	$10.82	$10.80	$10.80
Purchase #2	$152.73	13.440%	$173.2569	$173.26	$173.25	$173.30
Purchase #3	$171.82	12.191%	$192.7666	$192.77	$192.75	$192.80
Purchase #4	$59.91	7.678%	$64.5099	$64.51	$64.50	$64.50
Purchase #5	$60.75	11.755%	$67.8912	$67.89	$67.90	$67.90
Purchase #6	$237.52	4.781%	$248.8758	$248.88	$248.90	$248.90
Purchase #7	$57.94	6.216%	$61.5416	$61.54	$61.55	$61.50
7 purchase totals =	$750.18		$819.6597	$819.67	$819.65	$819.70