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	$166.73	7.249%	$178.8163	$178.82	$178.80	$178.80
Purchase #2	$73.96	4.838%	$77.5382	$77.54	$77.55	$77.50
Purchase #3	$71.61	12.519%	$80.5749	$80.57	$80.55	$80.60
Purchase #4	$54.59	12.753%	$61.5519	$61.55	$61.55	$61.60
Purchase #5	$27.61	11.338%	$30.7404	$30.74	$30.75	$30.70
Purchase #6	$170.97	9.723%	$187.5934	$187.59	$187.60	$187.60
Purchase #7	$73.69	11.766%	$82.3604	$82.36	$82.35	$82.40
7 purchase totals =	$639.16		$699.1755	$699.17	$699.15	$699.20