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	$201.35	13.146%	$227.8195	$227.82	$227.80	$227.80
Purchase #2	$64.60	11.634%	$72.1156	$72.12	$72.10	$72.10
Purchase #3	$23.46	5.692%	$24.7953	$24.80	$24.80	$24.80
Purchase #4	$107.74	3.270%	$111.2631	$111.26	$111.25	$111.30
Purchase #5	$62.61	8.171%	$67.7259	$67.73	$67.75	$67.70
Purchase #6	$102.34	8.488%	$111.0266	$111.03	$111.05	$111.00
Purchase #7	$202.51	3.335%	$209.2637	$209.26	$209.25	$209.30
7 purchase totals =	$764.61		$824.0097	$824.02	$824.00	$824.00