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	$85.25	3.587%	$88.3079	$88.31	$88.30	$88.30
Purchase #2	$97.42	12.305%	$109.4075	$109.41	$109.40	$109.40
Purchase #3	$167.82	8.151%	$181.499	$181.50	$181.50	$181.50
Purchase #4	$38.56	12.386%	$43.336	$43.34	$43.35	$43.30
Purchase #5	$46.37	7.786%	$49.9804	$49.98	$50.00	$50.00
Purchase #6	$46.74	4.708%	$48.9405	$48.94	$48.95	$48.90
Purchase #7	$68.66	6.758%	$73.3	$73.30	$73.30	$73.30
7 purchase totals =	$550.82		$594.7713	$594.78	$594.80	$594.70