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	$24.81	10.237%	$27.3498	$27.35	$27.35	$27.30
Purchase #2	$29.97	9.653%	$32.863	$32.86	$32.85	$32.90
Purchase #3	$118.74	13.499%	$134.7687	$134.77	$134.75	$134.80
Purchase #4	$41.53	11.697%	$46.3878	$46.39	$46.40	$46.40
Purchase #5	$37.96	8.616%	$41.2306	$41.23	$41.25	$41.20
Purchase #6	$97.25	9.148%	$106.1464	$106.15	$106.15	$106.10
Purchase #7	$38.43	10.559%	$42.4878	$42.49	$42.50	$42.50
7 purchase totals =	$388.69		$431.2341	$431.24	$431.25	$431.20