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	$230.69	10.602%	$255.1478	$255.15	$255.15	$255.10
Purchase #2	$27.53	9.415%	$30.1219	$30.12	$30.10	$30.10
Purchase #3	$196.74	12.827%	$221.9758	$221.98	$222.00	$222.00
Purchase #4	$219.29	4.267%	$228.6471	$228.65	$228.65	$228.60
Purchase #5	$218.46	4.146%	$227.5174	$227.52	$227.50	$227.50
Purchase #6	$94.52	7.764%	$101.8585	$101.86	$101.85	$101.90
Purchase #7	$236.31	3.820%	$245.337	$245.34	$245.35	$245.30
7 purchase totals =	$1,223.54		$1,310.6055	$1,310.62	$1,310.60	$1,310.50