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	$47.67	6.154%	$50.6036	$50.60	$50.60	$50.60
Purchase #2	$74.89	5.297%	$78.8569	$78.86	$78.85	$78.90
Purchase #3	$134.43	12.338%	$151.016	$151.02	$151.00	$151.00
Purchase #4	$100.95	7.579%	$108.601	$108.60	$108.60	$108.60
Purchase #5	$58.64	8.257%	$63.4819	$63.48	$63.50	$63.50
Purchase #6	$219.89	4.155%	$229.0264	$229.03	$229.05	$229.00
Purchase #7	$199.59	4.715%	$209.0007	$209.00	$209.00	$209.00
7 purchase totals =	$836.06		$890.5865	$890.59	$890.60	$890.60