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	$51.83	11.404%	$57.7407	$57.74	$57.75	$57.70
Purchase #2	$152.72	3.808%	$158.5356	$158.54	$158.55	$158.50
Purchase #3	$75.39	9.566%	$82.6018	$82.60	$82.60	$82.60
Purchase #4	$63.31	13.368%	$71.7733	$71.77	$71.75	$71.80
Purchase #5	$56.81	5.223%	$59.7772	$59.78	$59.80	$59.80
Purchase #6	$111.59	13.684%	$126.86	$126.86	$126.85	$126.90
Purchase #7	$188.44	10.865%	$208.914	$208.91	$208.90	$208.90
7 purchase totals =	$700.09		$766.2026	$766.20	$766.20	$766.20