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	$28.44	11.129%	$31.6051	$31.61	$31.60	$31.60
Purchase #2	$68.36	9.426%	$74.8036	$74.80	$74.80	$74.80
Purchase #3	$94.57	8.873%	$102.9612	$102.96	$102.95	$103.00
Purchase #4	$57.51	9.327%	$62.874	$62.87	$62.85	$62.90
Purchase #5	$83.25	7.300%	$89.3273	$89.33	$89.35	$89.30
Purchase #6	$95.45	8.719%	$103.7723	$103.77	$103.75	$103.80
Purchase #7	$194.48	7.237%	$208.5545	$208.55	$208.55	$208.60
7 purchase totals =	$622.06		$673.8980	$673.89	$673.85	$674.00