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	$182.73	3.352%	$188.8551	$188.86	$188.85	$188.90
Purchase #2	$154.30	8.481%	$167.3862	$167.39	$167.40	$167.40
Purchase #3	$246.69	11.634%	$275.3899	$275.39	$275.40	$275.40
Purchase #4	$148.46	9.628%	$162.7537	$162.75	$162.75	$162.80
Purchase #5	$178.69	12.222%	$200.5295	$200.53	$200.55	$200.50
Purchase #6	$146.97	9.607%	$161.0894	$161.09	$161.10	$161.10
Purchase #7	$78.42	5.619%	$82.8264	$82.83	$82.85	$82.80
7 purchase totals =	$1,136.26		$1,238.8302	$1,238.84	$1,238.90	$1,238.90