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	$170.89	11.758%	$190.9832	$190.98	$191.00	$191.00
Purchase #2	$214.84	11.198%	$238.8978	$238.90	$238.90	$238.90
Purchase #3	$37.85	11.343%	$42.1433	$42.14	$42.15	$42.10
Purchase #4	$128.78	7.605%	$138.5737	$138.57	$138.55	$138.60
Purchase #5	$30.54	3.491%	$31.6062	$31.61	$31.60	$31.60
Purchase #6	$126.44	3.866%	$131.3282	$131.33	$131.35	$131.30
Purchase #7	$11.98	11.139%	$13.3145	$13.31	$13.30	$13.30
7 purchase totals =	$721.32		$786.8469	$786.84	$786.85	$786.80