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	$136.56	4.552%	$142.7762	$142.78	$142.80	$142.80
Purchase #2	$92.63	8.160%	$100.1886	$100.19	$100.20	$100.20
Purchase #3	$164.42	3.870%	$170.7831	$170.78	$170.80	$170.80
Purchase #4	$142.67	7.760%	$153.7412	$153.74	$153.75	$153.70
Purchase #5	$43.91	12.326%	$49.3223	$49.32	$49.30	$49.30
Purchase #6	$99.40	12.466%	$111.7912	$111.79	$111.80	$111.80
Purchase #7	$190.33	11.604%	$212.4159	$212.42	$212.40	$212.40
7 purchase totals =	$869.92		$941.0185	$941.02	$941.05	$941.00