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	$165.61	12.160%	$185.7482	$185.75	$185.75	$185.70
Purchase #2	$16.45	9.467%	$18.0073	$18.01	$18.00	$18.00
Purchase #3	$79.55	13.406%	$90.2145	$90.21	$90.20	$90.20
Purchase #4	$72.27	12.464%	$81.2777	$81.28	$81.30	$81.30
Purchase #5	$159.32	10.235%	$175.6264	$175.63	$175.65	$175.60
Purchase #6	$28.29	11.798%	$31.6277	$31.63	$31.65	$31.60
Purchase #7	$93.91	5.789%	$99.3464	$99.35	$99.35	$99.30
7 purchase totals =	$615.40		$681.8482	$681.86	$681.90	$681.70