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	$105.42	11.343%	$117.3778	$117.38	$117.40	$117.40
Purchase #2	$56.25	6.374%	$59.8354	$59.84	$59.85	$59.80
Purchase #3	$245.33	3.303%	$253.4332	$253.43	$253.45	$253.40
Purchase #4	$31.93	11.436%	$35.5815	$35.58	$35.60	$35.60
Purchase #5	$219.98	11.770%	$245.8716	$245.87	$245.85	$245.90
Purchase #6	$230.94	8.127%	$249.7085	$249.71	$249.70	$249.70
Purchase #7	$36.81	7.296%	$39.4957	$39.50	$39.50	$39.50
7 purchase totals =	$926.66		$1,001.3037	$1,001.31	$1,001.35	$1,001.30