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	$221.51	9.353%	$242.2278	$242.23	$242.25	$242.20
Purchase #2	$148.40	13.305%	$168.1446	$168.14	$168.15	$168.10
Purchase #3	$94.65	11.272%	$105.3189	$105.32	$105.30	$105.30
Purchase #4	$70.89	13.461%	$80.4325	$80.43	$80.45	$80.40
Purchase #5	$103.41	12.152%	$115.9764	$115.98	$116.00	$116.00
Purchase #6	$141.69	9.265%	$154.8176	$154.82	$154.80	$154.80
Purchase #7	$91.33	8.714%	$99.2885	$99.29	$99.30	$99.30
7 purchase totals =	$871.88		$966.2063	$966.21	$966.25	$966.10