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	$55.89	9.399%	$61.1431	$61.14	$61.15	$61.10
Purchase #2	$74.98	8.556%	$81.3953	$81.40	$81.40	$81.40
Purchase #3	$164.98	12.229%	$185.1554	$185.16	$185.15	$185.20
Purchase #4	$72.79	8.275%	$78.8134	$78.81	$78.80	$78.80
Purchase #5	$39.40	11.235%	$43.8266	$43.83	$43.85	$43.80
Purchase #6	$16.67	7.461%	$17.9137	$17.91	$17.90	$17.90
Purchase #7	$106.71	5.533%	$112.6143	$112.61	$112.60	$112.60
7 purchase totals =	$531.42		$580.8618	$580.86	$580.85	$580.80