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	$6.76	10.826%	$7.4918	$7.49	$7.50	$7.50
Purchase #2	$16.87	7.377%	$18.1145	$18.11	$18.10	$18.10
Purchase #3	$103.36	8.658%	$112.3089	$112.31	$112.30	$112.30
Purchase #4	$210.36	11.488%	$234.5262	$234.53	$234.55	$234.50
Purchase #5	$77.27	10.817%	$85.6283	$85.63	$85.65	$85.60
Purchase #6	$180.35	7.668%	$194.1792	$194.18	$194.20	$194.20
Purchase #7	$55.95	11.851%	$62.5806	$62.58	$62.60	$62.60
7 purchase totals =	$650.92		$714.8295	$714.83	$714.90	$714.80