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	$91.31	3.518%	$94.5223	$94.52	$94.50	$94.50
Purchase #2	$248.72	7.846%	$268.2346	$268.23	$268.25	$268.20
Purchase #3	$101.29	10.725%	$112.1534	$112.15	$112.15	$112.20
Purchase #4	$156.90	6.279%	$166.7518	$166.75	$166.75	$166.80
Purchase #5	$138.62	10.558%	$153.2555	$153.26	$153.25	$153.30
Purchase #6	$229.41	11.207%	$255.12	$255.12	$255.10	$255.10
Purchase #7	$76.43	3.291%	$78.9453	$78.95	$78.95	$78.90
7 purchase totals =	$1,042.68		$1,128.9829	$1,128.98	$1,128.95	$1,129.00