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	$121.83	5.210%	$128.1773	$128.18	$128.20	$128.20
Purchase #2	$70.77	10.289%	$78.0515	$78.05	$78.05	$78.10
Purchase #3	$30.41	7.228%	$32.608	$32.61	$32.60	$32.60
Purchase #4	$91.61	8.506%	$99.4023	$99.40	$99.40	$99.40
Purchase #5	$152.94	6.129%	$162.3137	$162.31	$162.30	$162.30
Purchase #6	$248.44	8.302%	$269.0655	$269.07	$269.05	$269.10
Purchase #7	$74.50	5.542%	$78.6288	$78.63	$78.65	$78.60
7 purchase totals =	$790.50		$848.2471	$848.25	$848.25	$848.30