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	$60.45	12.284%	$67.8757	$67.88	$67.90	$67.90
Purchase #2	$142.33	9.171%	$155.3831	$155.38	$155.40	$155.40
Purchase #3	$190.56	12.755%	$214.8659	$214.87	$214.85	$214.90
Purchase #4	$23.25	3.745%	$24.1207	$24.12	$24.10	$24.10
Purchase #5	$172.89	8.524%	$187.6271	$187.63	$187.65	$187.60
Purchase #6	$81.73	10.408%	$90.2365	$90.24	$90.25	$90.20
Purchase #7	$81.51	13.491%	$92.5065	$92.51	$92.50	$92.50
7 purchase totals =	$752.72		$832.6155	$832.63	$832.65	$832.60