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	$26.33	3.661%	$27.2939	$27.29	$27.30	$27.30
Purchase #2	$128.48	11.780%	$143.6149	$143.61	$143.60	$143.60
Purchase #3	$82.54	10.589%	$91.2802	$91.28	$91.30	$91.30
Purchase #4	$187.62	8.141%	$202.8941	$202.89	$202.90	$202.90
Purchase #5	$227.63	3.149%	$234.7981	$234.80	$234.80	$234.80
Purchase #6	$181.32	5.259%	$190.8556	$190.86	$190.85	$190.90
Purchase #7	$180.67	10.225%	$199.1435	$199.14	$199.15	$199.10
7 purchase totals =	$1,014.59		$1,089.8803	$1,089.87	$1,089.90	$1,089.90