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	$221.47	13.746%	$251.9133	$251.91	$251.90	$251.90
Purchase #2	$88.95	4.448%	$92.9065	$92.91	$92.90	$92.90
Purchase #3	$63.94	11.242%	$71.1281	$71.13	$71.15	$71.10
Purchase #4	$162.65	12.673%	$183.2626	$183.26	$183.25	$183.30
Purchase #5	$58.87	11.189%	$65.457	$65.46	$65.45	$65.50
Purchase #6	$206.43	10.459%	$228.0205	$228.02	$228.00	$228.00
Purchase #7	$78.77	4.541%	$82.3469	$82.35	$82.35	$82.30
7 purchase totals =	$881.08		$975.0349	$975.04	$975.00	$975.00