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	$53.45	13.240%	$60.5268	$60.53	$60.55	$60.50
Purchase #2	$71.26	10.792%	$78.9504	$78.95	$78.95	$79.00
Purchase #3	$31.84	4.488%	$33.269	$33.27	$33.25	$33.30
Purchase #4	$178.78	7.281%	$191.797	$191.80	$191.80	$191.80
Purchase #5	$32.78	8.371%	$35.524	$35.52	$35.50	$35.50
Purchase #6	$59.35	8.302%	$64.2772	$64.28	$64.30	$64.30
Purchase #7	$129.54	3.558%	$134.149	$134.15	$134.15	$134.10
7 purchase totals =	$557.00		$598.4934	$598.50	$598.50	$598.50