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	$235.89	4.240%	$245.8917	$245.89	$245.90	$245.90
Purchase #2	$145.87	12.494%	$164.095	$164.10	$164.10	$164.10
Purchase #3	$78.72	8.391%	$85.3254	$85.33	$85.35	$85.30
Purchase #4	$26.71	3.120%	$27.5434	$27.54	$27.55	$27.50
Purchase #5	$134.72	7.464%	$144.7755	$144.78	$144.80	$144.80
Purchase #6	$113.35	12.140%	$127.1107	$127.11	$127.10	$127.10
Purchase #7	$123.99	6.287%	$131.7853	$131.79	$131.80	$131.80
7 purchase totals =	$859.25		$926.5270	$926.54	$926.60	$926.50