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	$103.61	5.248%	$109.0475	$109.05	$109.05	$109.00
Purchase #2	$77.75	13.445%	$88.2035	$88.20	$88.20	$88.20
Purchase #3	$24.78	13.520%	$28.1303	$28.13	$28.15	$28.10
Purchase #4	$188.51	4.561%	$197.1079	$197.11	$197.10	$197.10
Purchase #5	$156.47	10.510%	$172.915	$172.92	$172.90	$172.90
Purchase #6	$189.37	3.692%	$196.3615	$196.36	$196.35	$196.40
Purchase #7	$77.89	4.417%	$81.3304	$81.33	$81.35	$81.30
7 purchase totals =	$818.38		$873.0961	$873.10	$873.10	$873.00