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	$24.25	12.642%	$27.3157	$27.32	$27.30	$27.30
Purchase #2	$166.60	13.180%	$188.5579	$188.56	$188.55	$188.60
Purchase #3	$107.41	12.466%	$120.7997	$120.80	$120.80	$120.80
Purchase #4	$33.78	8.689%	$36.7151	$36.72	$36.70	$36.70
Purchase #5	$46.36	9.636%	$50.8272	$50.83	$50.85	$50.80
Purchase #6	$57.76	3.380%	$59.7123	$59.71	$59.70	$59.70
Purchase #7	$212.56	13.870%	$242.0421	$242.04	$242.05	$242.00
7 purchase totals =	$648.72		$725.9700	$725.98	$725.95	$725.90