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	$45.99	3.754%	$47.7165	$47.72	$47.70	$47.70
Purchase #2	$220.32	6.413%	$234.4491	$234.45	$234.45	$234.40
Purchase #3	$43.49	8.789%	$47.3123	$47.31	$47.30	$47.30
Purchase #4	$188.90	10.869%	$209.4315	$209.43	$209.45	$209.40
Purchase #5	$91.57	9.358%	$100.1391	$100.14	$100.15	$100.10
Purchase #6	$153.56	12.338%	$172.5062	$172.51	$172.50	$172.50
Purchase #7	$127.35	7.836%	$137.3291	$137.33	$137.35	$137.30
7 purchase totals =	$871.18		$948.8838	$948.89	$948.90	$948.70