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	$15.69	12.632%	$17.672	$17.67	$17.65	$17.70
Purchase #2	$30.79	7.553%	$33.1156	$33.12	$33.10	$33.10
Purchase #3	$123.30	3.269%	$127.3307	$127.33	$127.35	$127.30
Purchase #4	$246.81	7.110%	$264.3582	$264.36	$264.35	$264.40
Purchase #5	$65.88	6.277%	$70.0153	$70.02	$70.00	$70.00
Purchase #6	$145.85	11.150%	$162.1123	$162.11	$162.10	$162.10
Purchase #7	$238.95	10.456%	$263.9346	$263.93	$263.95	$263.90
7 purchase totals =	$867.27		$938.5387	$938.54	$938.50	$938.50