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	$82.52	8.622%	$89.6349	$89.63	$89.65	$89.60
Purchase #2	$84.58	5.263%	$89.0314	$89.03	$89.05	$89.00
Purchase #3	$5.67	5.442%	$5.9786	$5.98	$6.00	$6.00
Purchase #4	$202.62	13.113%	$229.1896	$229.19	$229.20	$229.20
Purchase #5	$206.90	7.713%	$222.8582	$222.86	$222.85	$222.90
Purchase #6	$99.53	12.176%	$111.6488	$111.65	$111.65	$111.60
Purchase #7	$43.27	5.850%	$45.8013	$45.80	$45.80	$45.80
7 purchase totals =	$725.09		$794.1428	$794.14	$794.20	$794.10