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	$117.31	8.314%	$127.0632	$127.06	$127.05	$127.10
Purchase #2	$89.47	11.548%	$99.802	$99.80	$99.80	$99.80
Purchase #3	$90.58	9.341%	$99.0411	$99.04	$99.05	$99.00
Purchase #4	$83.97	11.800%	$93.8785	$93.88	$93.90	$93.90
Purchase #5	$168.35	13.552%	$191.1648	$191.16	$191.15	$191.20
Purchase #6	$82.78	13.295%	$93.7856	$93.79	$93.80	$93.80
Purchase #7	$227.40	3.239%	$234.7655	$234.77	$234.75	$234.80
7 purchase totals =	$859.86		$939.5007	$939.50	$939.50	$939.60