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	$180.28	5.540%	$190.2675	$190.27	$190.25	$190.30
Purchase #2	$45.47	3.207%	$46.9282	$46.93	$46.95	$46.90
Purchase #3	$86.88	13.321%	$98.4533	$98.45	$98.45	$98.50
Purchase #4	$209.59	5.459%	$221.0315	$221.03	$221.05	$221.00
Purchase #5	$67.92	5.859%	$71.8994	$71.90	$71.90	$71.90
Purchase #6	$63.79	5.850%	$67.5217	$67.52	$67.50	$67.50
Purchase #7	$129.77	8.250%	$140.476	$140.48	$140.50	$140.50
7 purchase totals =	$783.70		$836.5776	$836.58	$836.60	$836.60