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	$229.98	12.265%	$258.187	$258.19	$258.20	$258.20
Purchase #2	$142.74	8.117%	$154.3262	$154.33	$154.35	$154.30
Purchase #3	$188.50	9.365%	$206.153	$206.15	$206.15	$206.20
Purchase #4	$239.93	6.825%	$256.3052	$256.31	$256.30	$256.30
Purchase #5	$48.66	7.277%	$52.201	$52.20	$52.20	$52.20
Purchase #6	$40.54	11.817%	$45.3306	$45.33	$45.35	$45.30
Purchase #7	$97.75	11.837%	$109.3207	$109.32	$109.30	$109.30
7 purchase totals =	$988.10		$1,081.8237	$1,081.83	$1,081.85	$1,081.80