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	$58.91	11.773%	$65.8455	$65.85	$65.85	$65.80
Purchase #2	$135.33	5.472%	$142.7353	$142.74	$142.75	$142.70
Purchase #3	$250.80	11.865%	$280.5574	$280.56	$280.55	$280.60
Purchase #4	$82.78	12.573%	$93.1879	$93.19	$93.20	$93.20
Purchase #5	$122.33	11.721%	$136.6683	$136.67	$136.65	$136.70
Purchase #6	$91.45	8.427%	$99.1565	$99.16	$99.15	$99.20
Purchase #7	$94.77	5.669%	$100.1425	$100.14	$100.15	$100.10
7 purchase totals =	$836.37		$918.2934	$918.31	$918.30	$918.30