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	$235.87	11.788%	$263.6744	$263.67	$263.65	$263.70
Purchase #2	$234.63	6.618%	$250.1578	$250.16	$250.15	$250.20
Purchase #3	$103.31	12.729%	$116.4603	$116.46	$116.45	$116.50
Purchase #4	$109.64	5.834%	$116.0364	$116.04	$116.05	$116.00
Purchase #5	$83.66	6.745%	$89.3029	$89.30	$89.30	$89.30
Purchase #6	$203.77	7.646%	$219.3503	$219.35	$219.35	$219.40
Purchase #7	$31.70	5.709%	$33.5098	$33.51	$33.50	$33.50
7 purchase totals =	$1,002.58		$1,088.4919	$1,088.49	$1,088.45	$1,088.60