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	$72.77	10.310%	$80.2726	$80.27	$80.25	$80.30
Purchase #2	$80.33	12.274%	$90.1897	$90.19	$90.20	$90.20
Purchase #3	$28.78	5.423%	$30.3407	$30.34	$30.35	$30.30
Purchase #4	$235.90	13.402%	$267.5153	$267.52	$267.50	$267.50
Purchase #5	$137.54	8.232%	$148.8623	$148.86	$148.85	$148.90
Purchase #6	$83.98	8.114%	$90.7941	$90.79	$90.80	$90.80
Purchase #7	$185.31	12.143%	$207.8122	$207.81	$207.80	$207.80
7 purchase totals =	$824.61		$915.7869	$915.78	$915.75	$915.80