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	$183.68	10.787%	$203.4936	$203.49	$203.50	$203.50
Purchase #2	$187.56	12.119%	$210.2904	$210.29	$210.30	$210.30
Purchase #3	$37.29	8.658%	$40.5186	$40.52	$40.50	$40.50
Purchase #4	$158.28	6.394%	$168.4004	$168.40	$168.40	$168.40
Purchase #5	$6.73	4.407%	$7.0266	$7.03	$7.05	$7.00
Purchase #6	$238.34	13.262%	$269.9487	$269.95	$269.95	$269.90
Purchase #7	$71.41	10.420%	$78.8509	$78.85	$78.85	$78.90
7 purchase totals =	$883.29		$978.5292	$978.53	$978.55	$978.50