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	$137.66	3.369%	$142.2978	$142.30	$142.30	$142.30
Purchase #2	$61.28	10.404%	$67.6556	$67.66	$67.65	$67.70
Purchase #3	$92.89	3.397%	$96.0455	$96.05	$96.05	$96.00
Purchase #4	$56.33	5.588%	$59.4777	$59.48	$59.50	$59.50
Purchase #5	$42.65	5.719%	$45.0892	$45.09	$45.10	$45.10
Purchase #6	$118.44	3.709%	$122.8329	$122.83	$122.85	$122.80
Purchase #7	$82.80	8.747%	$90.0425	$90.04	$90.05	$90.00
7 purchase totals =	$592.05		$623.4412	$623.45	$623.50	$623.40