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	$81.88	11.182%	$91.0358	$91.04	$91.05	$91.00
Purchase #2	$90.43	6.612%	$96.4092	$96.41	$96.40	$96.40
Purchase #3	$74.71	12.300%	$83.8993	$83.90	$83.90	$83.90
Purchase #4	$88.88	12.657%	$100.1295	$100.13	$100.15	$100.10
Purchase #5	$211.54	7.628%	$227.6763	$227.68	$227.70	$227.70
Purchase #6	$106.40	13.533%	$120.7991	$120.80	$120.80	$120.80
Purchase #7	$41.61	12.711%	$46.899	$46.90	$46.90	$46.90
7 purchase totals =	$695.45		$766.8482	$766.86	$766.90	$766.80