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	$123.95	6.110%	$131.5233	$131.52	$131.50	$131.50
Purchase #2	$245.36	4.268%	$255.832	$255.83	$255.85	$255.80
Purchase #3	$58.63	9.556%	$64.2327	$64.23	$64.25	$64.20
Purchase #4	$201.89	12.590%	$227.308	$227.31	$227.30	$227.30
Purchase #5	$57.92	3.334%	$59.8511	$59.85	$59.85	$59.90
Purchase #6	$56.30	10.388%	$62.1484	$62.15	$62.15	$62.10
Purchase #7	$93.60	9.519%	$102.5098	$102.51	$102.50	$102.50
7 purchase totals =	$837.65		$903.4053	$903.40	$903.40	$903.30