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	$93.63	8.351%	$101.449	$101.45	$101.45	$101.40
Purchase #2	$182.73	4.810%	$191.5193	$191.52	$191.50	$191.50
Purchase #3	$185.36	13.203%	$209.8331	$209.83	$209.85	$209.80
Purchase #4	$92.52	11.215%	$102.8961	$102.90	$102.90	$102.90
Purchase #5	$35.56	6.150%	$37.7469	$37.75	$37.75	$37.70
Purchase #6	$89.95	5.807%	$95.1734	$95.17	$95.15	$95.20
Purchase #7	$83.68	10.467%	$92.4388	$92.44	$92.45	$92.40
7 purchase totals =	$763.43		$831.0566	$831.06	$831.05	$830.90