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	$139.73	7.229%	$149.8311	$149.83	$149.85	$149.80
Purchase #2	$243.91	8.392%	$264.3789	$264.38	$264.40	$264.40
Purchase #3	$12.57	5.752%	$13.293	$13.29	$13.30	$13.30
Purchase #4	$238.65	4.727%	$249.931	$249.93	$249.95	$249.90
Purchase #5	$43.57	3.583%	$45.1311	$45.13	$45.15	$45.10
Purchase #6	$80.55	6.202%	$85.5457	$85.55	$85.55	$85.50
Purchase #7	$27.42	3.391%	$28.3498	$28.35	$28.35	$28.30
7 purchase totals =	$786.40		$836.4606	$836.46	$836.55	$836.30