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	$153.76	10.657%	$170.1462	$170.15	$170.15	$170.10
Purchase #2	$236.27	5.448%	$249.142	$249.14	$249.15	$249.10
Purchase #3	$62.43	13.148%	$70.6383	$70.64	$70.65	$70.60
Purchase #4	$53.88	11.231%	$59.9313	$59.93	$59.95	$59.90
Purchase #5	$15.61	6.196%	$16.5772	$16.58	$16.60	$16.60
Purchase #6	$68.61	10.632%	$75.9046	$75.90	$75.90	$75.90
Purchase #7	$63.91	13.179%	$72.3327	$72.33	$72.35	$72.30
7 purchase totals =	$654.47		$714.6723	$714.67	$714.75	$714.50