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	$30.52	8.679%	$33.1688	$33.17	$33.15	$33.20
Purchase #2	$39.77	9.159%	$43.4125	$43.41	$43.40	$43.40
Purchase #3	$172.70	7.363%	$185.4159	$185.42	$185.40	$185.40
Purchase #4	$10.86	5.345%	$11.4405	$11.44	$11.45	$11.40
Purchase #5	$137.54	3.131%	$141.8464	$141.85	$141.85	$141.80
Purchase #6	$28.83	5.423%	$30.3935	$30.39	$30.40	$30.40
Purchase #7	$172.56	8.198%	$186.7065	$186.71	$186.70	$186.70
7 purchase totals =	$592.78		$632.3841	$632.39	$632.35	$632.30