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	$73.79	10.240%	$81.3461	$81.35	$81.35	$81.30
Purchase #2	$134.82	9.585%	$147.7425	$147.74	$147.75	$147.70
Purchase #3	$128.88	8.513%	$139.8516	$139.85	$139.85	$139.90
Purchase #4	$55.73	10.851%	$61.7773	$61.78	$61.80	$61.80
Purchase #5	$186.83	3.147%	$192.7095	$192.71	$192.70	$192.70
Purchase #6	$77.84	7.575%	$83.7364	$83.74	$83.75	$83.70
Purchase #7	$121.50	4.728%	$127.2445	$127.24	$127.25	$127.20
7 purchase totals =	$779.39		$834.4079	$834.41	$834.45	$834.30