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	$164.47	6.851%	$175.7378	$175.74	$175.75	$175.70
Purchase #2	$79.87	12.774%	$90.0726	$90.07	$90.05	$90.10
Purchase #3	$222.79	12.568%	$250.7902	$250.79	$250.80	$250.80
Purchase #4	$211.75	13.554%	$240.4506	$240.45	$240.45	$240.50
Purchase #5	$17.85	13.735%	$20.3017	$20.30	$20.30	$20.30
Purchase #6	$50.80	12.834%	$57.3197	$57.32	$57.30	$57.30
Purchase #7	$63.86	11.123%	$70.9631	$70.96	$70.95	$71.00
7 purchase totals =	$811.39		$905.6357	$905.63	$905.60	$905.70