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	$234.31	10.687%	$259.3507	$259.35	$259.35	$259.40
Purchase #2	$78.79	3.582%	$81.6123	$81.61	$81.60	$81.60
Purchase #3	$90.84	7.816%	$97.9401	$97.94	$97.95	$97.90
Purchase #4	$79.94	6.613%	$85.2264	$85.23	$85.25	$85.20
Purchase #5	$48.37	13.710%	$55.0015	$55.00	$55.00	$55.00
Purchase #6	$129.90	7.215%	$139.2723	$139.27	$139.25	$139.30
Purchase #7	$91.54	4.345%	$95.5174	$95.52	$95.50	$95.50
7 purchase totals =	$753.69		$813.9207	$813.92	$813.90	$813.90