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	$161.93	6.772%	$172.8959	$172.90	$172.90	$172.90
Purchase #2	$106.61	9.802%	$117.0599	$117.06	$117.05	$117.10
Purchase #3	$140.81	6.735%	$150.2936	$150.29	$150.30	$150.30
Purchase #4	$92.25	7.755%	$99.404	$99.40	$99.40	$99.40
Purchase #5	$101.42	11.632%	$113.2172	$113.22	$113.20	$113.20
Purchase #6	$28.63	10.488%	$31.6327	$31.63	$31.65	$31.60
Purchase #7	$123.27	12.515%	$138.6972	$138.70	$138.70	$138.70
7 purchase totals =	$754.92		$823.2005	$823.20	$823.20	$823.20