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	$173.33	9.495%	$189.7877	$189.79	$189.80	$189.80
Purchase #2	$90.61	9.866%	$99.5496	$99.55	$99.55	$99.50
Purchase #3	$64.31	10.679%	$71.1777	$71.18	$71.20	$71.20
Purchase #4	$107.88	4.121%	$112.3257	$112.33	$112.35	$112.30
Purchase #5	$86.34	3.574%	$89.4258	$89.43	$89.45	$89.40
Purchase #6	$230.27	8.177%	$249.0992	$249.10	$249.10	$249.10
Purchase #7	$121.58	5.566%	$128.3471	$128.35	$128.35	$128.30
7 purchase totals =	$874.32		$939.7128	$939.73	$939.80	$939.60