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	$185.60	6.103%	$196.9272	$196.93	$196.95	$196.90
Purchase #2	$238.67	12.763%	$269.1315	$269.13	$269.15	$269.10
Purchase #3	$95.49	4.235%	$99.534	$99.53	$99.55	$99.50
Purchase #4	$61.37	10.232%	$67.6494	$67.65	$67.65	$67.60
Purchase #5	$88.64	8.553%	$96.2214	$96.22	$96.20	$96.20
Purchase #6	$125.55	11.442%	$139.9154	$139.92	$139.90	$139.90
Purchase #7	$108.48	6.357%	$115.3761	$115.38	$115.40	$115.40
7 purchase totals =	$903.80		$984.7550	$984.76	$984.80	$984.60