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	$54.53	8.470%	$59.1487	$59.15	$59.15	$59.10
Purchase #2	$25.93	13.125%	$29.3333	$29.33	$29.35	$29.30
Purchase #3	$25.56	7.849%	$27.5662	$27.57	$27.55	$27.60
Purchase #4	$149.49	11.632%	$166.8787	$166.88	$166.90	$166.90
Purchase #5	$85.74	4.317%	$89.4414	$89.44	$89.45	$89.40
Purchase #6	$144.41	11.530%	$161.0605	$161.06	$161.05	$161.10
Purchase #7	$134.33	5.649%	$141.9183	$141.92	$141.90	$141.90
7 purchase totals =	$619.99		$675.3471	$675.35	$675.35	$675.30