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	$55.84	6.499%	$59.469	$59.47	$59.45	$59.50
Purchase #2	$198.46	13.820%	$225.8872	$225.89	$225.90	$225.90
Purchase #3	$73.45	8.163%	$79.4457	$79.45	$79.45	$79.40
Purchase #4	$75.67	7.271%	$81.172	$81.17	$81.15	$81.20
Purchase #5	$142.99	10.727%	$158.3285	$158.33	$158.35	$158.30
Purchase #6	$88.81	6.183%	$94.3011	$94.30	$94.30	$94.30
Purchase #7	$13.45	10.500%	$14.8623	$14.86	$14.85	$14.90
7 purchase totals =	$648.67		$713.4658	$713.47	$713.45	$713.50