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	$47.65	12.321%	$53.521	$53.52	$53.50	$53.50
Purchase #2	$148.94	13.152%	$168.5286	$168.53	$168.55	$168.50
Purchase #3	$61.31	4.192%	$63.8801	$63.88	$63.90	$63.90
Purchase #4	$28.41	13.451%	$32.2314	$32.23	$32.25	$32.20
Purchase #5	$155.52	11.347%	$173.1669	$173.17	$173.15	$173.20
Purchase #6	$221.78	12.576%	$249.6711	$249.67	$249.65	$249.70
Purchase #7	$88.36	12.166%	$99.1099	$99.11	$99.10	$99.10
7 purchase totals =	$751.97		$840.1090	$840.11	$840.10	$840.10