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	$53.45	8.282%	$57.8767	$57.88	$57.90	$57.90
Purchase #2	$113.38	11.579%	$126.5083	$126.51	$126.50	$126.50
Purchase #3	$168.60	6.734%	$179.9535	$179.95	$179.95	$180.00
Purchase #4	$110.87	7.132%	$118.7772	$118.78	$118.80	$118.80
Purchase #5	$34.67	6.305%	$36.8559	$36.86	$36.85	$36.90
Purchase #6	$167.47	12.588%	$188.5511	$188.55	$188.55	$188.60
Purchase #7	$114.36	11.494%	$127.5045	$127.50	$127.50	$127.50
7 purchase totals =	$762.80		$836.0272	$836.03	$836.05	$836.20