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	$39.83	7.264%	$42.7233	$42.72	$42.70	$42.70
Purchase #2	$225.82	11.678%	$252.1913	$252.19	$252.20	$252.20
Purchase #3	$197.95	4.526%	$206.9092	$206.91	$206.90	$206.90
Purchase #4	$51.88	10.587%	$57.3725	$57.37	$57.35	$57.40
Purchase #5	$28.78	10.442%	$31.7852	$31.79	$31.80	$31.80
Purchase #6	$120.73	8.755%	$131.2999	$131.30	$131.30	$131.30
Purchase #7	$101.77	9.187%	$111.1196	$111.12	$111.10	$111.10
7 purchase totals =	$766.76		$833.4010	$833.40	$833.35	$833.40