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	$30.88	4.253%	$32.1933	$32.19	$32.20	$32.20
Purchase #2	$117.36	9.165%	$128.116	$128.12	$128.10	$128.10
Purchase #3	$92.88	7.870%	$100.1897	$100.19	$100.20	$100.20
Purchase #4	$224.75	11.420%	$250.4165	$250.42	$250.40	$250.40
Purchase #5	$83.35	9.809%	$91.5258	$91.53	$91.55	$91.50
Purchase #6	$151.39	7.348%	$162.5141	$162.51	$162.50	$162.50
Purchase #7	$6.75	10.191%	$7.4379	$7.44	$7.45	$7.40
7 purchase totals =	$707.36		$772.3933	$772.40	$772.40	$772.30