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	$101.84	4.359%	$106.2792	$106.28	$106.30	$106.30
Purchase #2	$162.85	6.528%	$173.4808	$173.48	$173.50	$173.50
Purchase #3	$49.56	12.368%	$55.6896	$55.69	$55.70	$55.70
Purchase #4	$137.32	7.452%	$147.5531	$147.55	$147.55	$147.60
Purchase #5	$151.75	5.641%	$160.3102	$160.31	$160.30	$160.30
Purchase #6	$131.79	7.547%	$141.7362	$141.74	$141.75	$141.70
Purchase #7	$103.78	5.511%	$109.4993	$109.50	$109.50	$109.50
7 purchase totals =	$838.89		$894.5484	$894.55	$894.60	$894.60