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	$139.76	3.439%	$144.5663	$144.57	$144.55	$144.60
Purchase #2	$89.98	11.198%	$100.056	$100.06	$100.05	$100.10
Purchase #3	$146.80	4.106%	$152.8276	$152.83	$152.85	$152.80
Purchase #4	$117.83	13.626%	$133.8855	$133.89	$133.90	$133.90
Purchase #5	$185.62	10.354%	$204.8391	$204.84	$204.85	$204.80
Purchase #6	$94.91	7.645%	$102.1659	$102.17	$102.15	$102.20
Purchase #7	$138.59	7.849%	$149.4679	$149.47	$149.45	$149.50
7 purchase totals =	$913.49		$987.8083	$987.83	$987.80	$987.90