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	$142.53	12.483%	$160.322	$160.32	$160.30	$160.30
Purchase #2	$143.87	12.200%	$161.4221	$161.42	$161.40	$161.40
Purchase #3	$158.79	6.574%	$169.2289	$169.23	$169.25	$169.20
Purchase #4	$96.69	13.614%	$109.8534	$109.85	$109.85	$109.90
Purchase #5	$72.92	6.532%	$77.6831	$77.68	$77.70	$77.70
Purchase #6	$198.81	3.143%	$205.0586	$205.06	$205.05	$205.10
Purchase #7	$246.81	3.852%	$256.3171	$256.32	$256.30	$256.30
7 purchase totals =	$1,060.42		$1,139.8852	$1,139.88	$1,139.85	$1,139.90