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	$122.28	10.868%	$135.5694	$135.57	$135.55	$135.60
Purchase #2	$213.28	4.289%	$222.4276	$222.43	$222.45	$222.40
Purchase #3	$209.32	7.439%	$224.8913	$224.89	$224.90	$224.90
Purchase #4	$28.26	6.763%	$30.1712	$30.17	$30.15	$30.20
Purchase #5	$66.87	8.397%	$72.4851	$72.49	$72.50	$72.50
Purchase #6	$39.73	9.823%	$43.6327	$43.63	$43.65	$43.60
Purchase #7	$33.99	10.730%	$37.6371	$37.64	$37.65	$37.60
7 purchase totals =	$713.73		$766.8144	$766.82	$766.85	$766.80