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	$78.61	12.691%	$88.5864	$88.59	$88.60	$88.60
Purchase #2	$236.55	8.121%	$255.7602	$255.76	$255.75	$255.80
Purchase #3	$191.45	9.602%	$209.833	$209.83	$209.85	$209.80
Purchase #4	$18.71	6.791%	$19.9806	$19.98	$20.00	$20.00
Purchase #5	$6.85	5.516%	$7.2278	$7.23	$7.25	$7.20
Purchase #6	$228.53	5.427%	$240.9323	$240.93	$240.95	$240.90
Purchase #7	$42.45	3.797%	$44.0618	$44.06	$44.05	$44.10
7 purchase totals =	$803.15		$866.3821	$866.38	$866.45	$866.40