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	$217.86	9.563%	$238.694	$238.69	$238.70	$238.70
Purchase #2	$192.34	13.807%	$218.8964	$218.90	$218.90	$218.90
Purchase #3	$144.89	9.747%	$159.0124	$159.01	$159.00	$159.00
Purchase #4	$168.86	8.532%	$183.2671	$183.27	$183.25	$183.30
Purchase #5	$90.30	13.150%	$102.1745	$102.17	$102.15	$102.20
Purchase #6	$135.38	11.813%	$151.3724	$151.37	$151.35	$151.40
Purchase #7	$230.38	12.380%	$258.901	$258.90	$258.90	$258.90
7 purchase totals =	$1,180.01		$1,312.3178	$1,312.31	$1,312.25	$1,312.40