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	$220.64	10.530%	$243.8734	$243.87	$243.85	$243.90
Purchase #2	$155.94	9.774%	$171.1816	$171.18	$171.20	$171.20
Purchase #3	$55.57	10.703%	$61.5177	$61.52	$61.50	$61.50
Purchase #4	$225.79	13.186%	$255.5627	$255.56	$255.55	$255.60
Purchase #5	$18.68	7.597%	$20.0991	$20.10	$20.10	$20.10
Purchase #6	$149.69	8.566%	$162.5124	$162.51	$162.50	$162.50
Purchase #7	$97.64	4.204%	$101.7448	$101.74	$101.75	$101.70
7 purchase totals =	$923.95		$1,016.4917	$1,016.48	$1,016.45	$1,016.50