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	$29.89	7.320%	$32.0779	$32.08	$32.10	$32.10
Purchase #2	$153.78	7.694%	$165.6118	$165.61	$165.60	$165.60
Purchase #3	$123.25	11.250%	$137.1156	$137.12	$137.10	$137.10
Purchase #4	$71.62	11.246%	$79.6744	$79.67	$79.65	$79.70
Purchase #5	$192.67	12.325%	$216.4166	$216.42	$216.40	$216.40
Purchase #6	$174.57	5.712%	$184.5414	$184.54	$184.55	$184.50
Purchase #7	$168.59	11.702%	$188.3184	$188.32	$188.30	$188.30
7 purchase totals =	$914.37		$1,003.7561	$1,003.76	$1,003.70	$1,003.70