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	$29.69	7.296%	$31.8562	$31.86	$31.85	$31.90
Purchase #2	$95.75	9.816%	$105.1488	$105.15	$105.15	$105.10
Purchase #3	$210.69	12.388%	$236.7903	$236.79	$236.80	$236.80
Purchase #4	$58.25	10.824%	$64.555	$64.56	$64.55	$64.60
Purchase #5	$49.98	5.816%	$52.8868	$52.89	$52.90	$52.90
Purchase #6	$135.98	3.798%	$141.1445	$141.14	$141.15	$141.10
Purchase #7	$120.55	4.782%	$126.3147	$126.31	$126.30	$126.30
7 purchase totals =	$700.89		$758.6963	$758.70	$758.70	$758.70