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	$35.96	7.771%	$38.7545	$38.75	$38.75	$38.80
Purchase #2	$153.35	7.497%	$164.8466	$164.85	$164.85	$164.80
Purchase #3	$225.47	5.573%	$238.0354	$238.04	$238.05	$238.00
Purchase #4	$14.93	6.280%	$15.8676	$15.87	$15.85	$15.90
Purchase #5	$219.75	6.437%	$233.8953	$233.90	$233.90	$233.90
Purchase #6	$236.32	13.487%	$268.1925	$268.19	$268.20	$268.20
Purchase #7	$39.67	8.808%	$43.1641	$43.16	$43.15	$43.20
7 purchase totals =	$925.45		$1,002.7560	$1,002.76	$1,002.75	$1,002.80