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	$92.34	6.756%	$98.5785	$98.58	$98.60	$98.60
Purchase #2	$114.83	13.540%	$130.378	$130.38	$130.40	$130.40
Purchase #3	$247.64	13.114%	$280.1155	$280.12	$280.10	$280.10
Purchase #4	$189.74	5.641%	$200.4432	$200.44	$200.45	$200.40
Purchase #5	$208.53	5.469%	$219.9345	$219.93	$219.95	$219.90
Purchase #6	$73.57	13.504%	$83.5049	$83.50	$83.50	$83.50
Purchase #7	$143.96	8.196%	$155.759	$155.76	$155.75	$155.80
7 purchase totals =	$1,070.61		$1,168.7136	$1,168.71	$1,168.75	$1,168.70