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	$69.96	11.608%	$78.081	$78.08	$78.10	$78.10
Purchase #2	$92.31	7.234%	$98.9877	$98.99	$99.00	$99.00
Purchase #3	$78.54	4.446%	$82.0319	$82.03	$82.05	$82.00
Purchase #4	$93.31	6.312%	$99.1997	$99.20	$99.20	$99.20
Purchase #5	$211.80	9.485%	$231.8892	$231.89	$231.90	$231.90
Purchase #6	$19.74	3.647%	$20.4599	$20.46	$20.45	$20.50
Purchase #7	$238.86	4.338%	$249.2217	$249.22	$249.20	$249.20
7 purchase totals =	$804.52		$859.8711	$859.87	$859.90	$859.90