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	$69.37	12.707%	$78.1848	$78.18	$78.20	$78.20
Purchase #2	$31.60	4.708%	$33.0877	$33.09	$33.10	$33.10
Purchase #3	$142.34	9.534%	$155.9107	$155.91	$155.90	$155.90
Purchase #4	$33.51	7.304%	$35.9576	$35.96	$35.95	$36.00
Purchase #5	$166.41	13.355%	$188.6341	$188.63	$188.65	$188.60
Purchase #6	$113.87	12.651%	$128.2757	$128.28	$128.30	$128.30
Purchase #7	$141.28	9.301%	$154.4205	$154.42	$154.40	$154.40
7 purchase totals =	$698.38		$774.4711	$774.47	$774.50	$774.50