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	$42.38	8.142%	$45.8306	$45.83	$45.85	$45.80
Purchase #2	$227.53	9.825%	$249.8848	$249.88	$249.90	$249.90
Purchase #3	$239.39	10.433%	$264.3656	$264.37	$264.35	$264.40
Purchase #4	$96.36	3.395%	$99.6314	$99.63	$99.65	$99.60
Purchase #5	$74.69	5.214%	$78.5843	$78.58	$78.60	$78.60
Purchase #6	$90.81	3.367%	$93.8676	$93.87	$93.85	$93.90
Purchase #7	$213.69	4.407%	$223.1073	$223.11	$223.10	$223.10
7 purchase totals =	$984.85		$1,055.2716	$1,055.27	$1,055.30	$1,055.30