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	$156.66	10.292%	$172.7834	$172.78	$172.80	$172.80
Purchase #2	$50.31	9.656%	$55.1679	$55.17	$55.15	$55.20
Purchase #3	$183.54	6.234%	$194.9819	$194.98	$195.00	$195.00
Purchase #4	$151.73	11.571%	$169.2867	$169.29	$169.30	$169.30
Purchase #5	$35.90	11.810%	$40.1398	$40.14	$40.15	$40.10
Purchase #6	$66.35	7.801%	$71.526	$71.53	$71.55	$71.50
Purchase #7	$89.25	4.491%	$93.2582	$93.26	$93.25	$93.30
7 purchase totals =	$733.74		$797.1439	$797.15	$797.20	$797.20