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	$104.56	11.790%	$116.8876	$116.89	$116.90	$116.90
Purchase #2	$238.69	6.310%	$253.7513	$253.75	$253.75	$253.80
Purchase #3	$101.57	12.136%	$113.8965	$113.90	$113.90	$113.90
Purchase #4	$58.74	5.282%	$61.8426	$61.84	$61.85	$61.80
Purchase #5	$87.83	13.807%	$99.9567	$99.96	$99.95	$100.00
Purchase #6	$180.70	8.604%	$196.2474	$196.25	$196.25	$196.20
Purchase #7	$149.39	5.398%	$157.4541	$157.45	$157.45	$157.50
7 purchase totals =	$921.48		$1,000.0362	$1,000.04	$1,000.05	$1,000.10