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	$28.71	5.622%	$30.3241	$30.32	$30.30	$30.30
Purchase #2	$80.95	12.256%	$90.8712	$90.87	$90.85	$90.90
Purchase #3	$169.92	5.642%	$179.5069	$179.51	$179.50	$179.50
Purchase #4	$109.42	12.450%	$123.0428	$123.04	$123.05	$123.00
Purchase #5	$210.64	5.814%	$222.8866	$222.89	$222.90	$222.90
Purchase #6	$90.32	8.141%	$97.673	$97.67	$97.65	$97.70
Purchase #7	$91.94	6.141%	$97.586	$97.59	$97.60	$97.60
7 purchase totals =	$781.90		$841.8906	$841.89	$841.85	$841.90