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	$79.93	13.573%	$90.7789	$90.78	$90.80	$90.80
Purchase #2	$75.77	13.206%	$85.7762	$85.78	$85.80	$85.80
Purchase #3	$164.65	9.534%	$180.3477	$180.35	$180.35	$180.30
Purchase #4	$96.79	12.453%	$108.8433	$108.84	$108.85	$108.80
Purchase #5	$234.89	12.828%	$265.0217	$265.02	$265.00	$265.00
Purchase #6	$67.96	8.749%	$73.9058	$73.91	$73.90	$73.90
Purchase #7	$12.45	5.566%	$13.143	$13.14	$13.15	$13.10
7 purchase totals =	$732.44		$817.8166	$817.82	$817.85	$817.70