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	$26.74	9.705%	$29.3351	$29.34	$29.35	$29.30
Purchase #2	$237.46	3.810%	$246.5072	$246.51	$246.50	$246.50
Purchase #3	$233.77	9.132%	$255.1179	$255.12	$255.10	$255.10
Purchase #4	$106.25	4.474%	$111.0036	$111.00	$111.00	$111.00
Purchase #5	$111.81	4.391%	$116.7196	$116.72	$116.70	$116.70
Purchase #6	$157.28	7.297%	$168.7567	$168.76	$168.75	$168.80
Purchase #7	$90.77	11.702%	$101.3919	$101.39	$101.40	$101.40
7 purchase totals =	$964.08		$1,028.8320	$1,028.84	$1,028.80	$1,028.80