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	$73.26	10.520%	$80.967	$80.97	$80.95	$81.00
Purchase #2	$228.56	4.273%	$238.3264	$238.33	$238.35	$238.30
Purchase #3	$34.71	9.641%	$38.0564	$38.06	$38.05	$38.10
Purchase #4	$237.78	7.358%	$255.2759	$255.28	$255.30	$255.30
Purchase #5	$202.73	9.712%	$222.4191	$222.42	$222.40	$222.40
Purchase #6	$18.80	9.437%	$20.5742	$20.57	$20.55	$20.60
Purchase #7	$32.77	11.340%	$36.4861	$36.49	$36.50	$36.50
7 purchase totals =	$828.61		$892.1051	$892.12	$892.10	$892.20