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	$45.86	10.149%	$50.5143	$50.51	$50.50	$50.50
Purchase #2	$8.46	6.636%	$9.0214	$9.02	$9.00	$9.00
Purchase #3	$89.49	12.446%	$100.6279	$100.63	$100.65	$100.60
Purchase #4	$203.61	9.649%	$223.2563	$223.26	$223.25	$223.30
Purchase #5	$91.36	10.463%	$100.919	$100.92	$100.90	$100.90
Purchase #6	$201.60	7.709%	$217.1413	$217.14	$217.15	$217.10
Purchase #7	$141.77	6.284%	$150.6788	$150.68	$150.70	$150.70
7 purchase totals =	$782.15		$852.1590	$852.16	$852.15	$852.10