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	$248.50	12.721%	$280.1117	$280.11	$280.10	$280.10
Purchase #2	$75.71	9.350%	$82.7889	$82.79	$82.80	$82.80
Purchase #3	$89.59	6.822%	$95.7018	$95.70	$95.70	$95.70
Purchase #4	$159.53	10.300%	$175.9616	$175.96	$175.95	$176.00
Purchase #5	$158.86	8.852%	$172.9223	$172.92	$172.90	$172.90
Purchase #6	$113.29	13.234%	$128.2828	$128.28	$128.30	$128.30
Purchase #7	$178.47	5.656%	$188.5643	$188.56	$188.55	$188.60
7 purchase totals =	$1,023.95		$1,124.3334	$1,124.32	$1,124.30	$1,124.40