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	$87.90	9.771%	$96.4887	$96.49	$96.50	$96.50
Purchase #2	$57.92	5.495%	$61.1027	$61.10	$61.10	$61.10
Purchase #3	$152.30	8.385%	$165.0704	$165.07	$165.05	$165.10
Purchase #4	$223.64	7.665%	$240.782	$240.78	$240.80	$240.80
Purchase #5	$169.96	9.134%	$185.4841	$185.48	$185.50	$185.50
Purchase #6	$30.43	10.581%	$33.6498	$33.65	$33.65	$33.60
Purchase #7	$134.38	10.693%	$148.7493	$148.75	$148.75	$148.70
7 purchase totals =	$856.53		$931.3270	$931.32	$931.35	$931.30