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	$83.30	8.679%	$90.5296	$90.53	$90.55	$90.50
Purchase #2	$143.70	11.237%	$159.8476	$159.85	$159.85	$159.80
Purchase #3	$61.34	10.628%	$67.8592	$67.86	$67.85	$67.90
Purchase #4	$131.62	12.465%	$148.0264	$148.03	$148.05	$148.00
Purchase #5	$228.82	11.834%	$255.8986	$255.90	$255.90	$255.90
Purchase #6	$31.45	6.831%	$33.5983	$33.60	$33.60	$33.60
Purchase #7	$156.74	6.523%	$166.9642	$166.96	$166.95	$167.00
7 purchase totals =	$836.97		$922.7239	$922.73	$922.75	$922.70