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	$78.59	4.519%	$82.1415	$82.14	$82.15	$82.10
Purchase #2	$75.31	6.616%	$80.2925	$80.29	$80.30	$80.30
Purchase #3	$118.45	8.416%	$128.4188	$128.42	$128.40	$128.40
Purchase #4	$87.39	3.689%	$90.6138	$90.61	$90.60	$90.60
Purchase #5	$14.61	7.199%	$15.6618	$15.66	$15.65	$15.70
Purchase #6	$169.74	8.520%	$184.2018	$184.20	$184.20	$184.20
Purchase #7	$89.33	11.414%	$99.5261	$99.53	$99.55	$99.50
7 purchase totals =	$633.42		$680.8563	$680.85	$680.85	$680.80