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	$91.52	8.783%	$99.5582	$99.56	$99.55	$99.60
Purchase #2	$87.38	6.440%	$93.0073	$93.01	$93.00	$93.00
Purchase #3	$186.34	7.766%	$200.8112	$200.81	$200.80	$200.80
Purchase #4	$28.41	3.197%	$29.3183	$29.32	$29.30	$29.30
Purchase #5	$128.59	3.215%	$132.7242	$132.72	$132.70	$132.70
Purchase #6	$59.72	7.213%	$64.0276	$64.03	$64.05	$64.00
Purchase #7	$222.41	10.654%	$246.1056	$246.11	$246.10	$246.10
7 purchase totals =	$804.37		$865.5524	$865.56	$865.50	$865.50