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	$94.85	5.852%	$100.4006	$100.40	$100.40	$100.40
Purchase #2	$43.87	9.730%	$48.1386	$48.14	$48.15	$48.10
Purchase #3	$223.98	6.591%	$238.7425	$238.74	$238.75	$238.70
Purchase #4	$90.78	9.439%	$99.3487	$99.35	$99.35	$99.30
Purchase #5	$33.98	5.160%	$35.7334	$35.73	$35.75	$35.70
Purchase #6	$99.31	10.731%	$109.967	$109.97	$109.95	$110.00
Purchase #7	$111.51	10.625%	$123.3579	$123.36	$123.35	$123.40
7 purchase totals =	$698.28		$755.6887	$755.69	$755.70	$755.60