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	$160.52	3.507%	$166.1494	$166.15	$166.15	$166.10
Purchase #2	$246.33	8.565%	$267.4282	$267.43	$267.45	$267.40
Purchase #3	$56.41	3.334%	$58.2907	$58.29	$58.30	$58.30
Purchase #4	$39.47	4.152%	$41.1088	$41.11	$41.10	$41.10
Purchase #5	$89.76	4.291%	$93.6116	$93.61	$93.60	$93.60
Purchase #6	$154.65	8.543%	$167.8617	$167.86	$167.85	$167.90
Purchase #7	$38.55	10.155%	$42.4648	$42.46	$42.45	$42.50
7 purchase totals =	$785.69		$836.9152	$836.91	$836.90	$836.90