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	$52.92	12.365%	$59.4636	$59.46	$59.45	$59.50
Purchase #2	$193.77	11.374%	$215.8094	$215.81	$215.80	$215.80
Purchase #3	$110.48	5.145%	$116.1642	$116.16	$116.15	$116.20
Purchase #4	$99.98	4.857%	$104.836	$104.84	$104.85	$104.80
Purchase #5	$206.32	13.276%	$233.711	$233.71	$233.70	$233.70
Purchase #6	$88.84	5.656%	$93.8648	$93.86	$93.85	$93.90
Purchase #7	$104.97	9.140%	$114.5643	$114.56	$114.55	$114.60
7 purchase totals =	$857.28		$938.4133	$938.40	$938.35	$938.50