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	$39.79	6.771%	$42.4842	$42.48	$42.50	$42.50
Purchase #2	$73.44	13.377%	$83.2641	$83.26	$83.25	$83.30
Purchase #3	$197.72	7.625%	$212.7962	$212.80	$212.80	$212.80
Purchase #4	$111.98	10.362%	$123.5834	$123.58	$123.60	$123.60
Purchase #5	$106.43	11.749%	$118.9345	$118.93	$118.95	$118.90
Purchase #6	$209.43	7.773%	$225.709	$225.71	$225.70	$225.70
Purchase #7	$97.34	12.269%	$109.2826	$109.28	$109.30	$109.30
7 purchase totals =	$836.13		$916.0540	$916.04	$916.10	$916.10