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	$47.44	12.861%	$53.5413	$53.54	$53.55	$53.50
Purchase #2	$42.78	7.171%	$45.8478	$45.85	$45.85	$45.80
Purchase #3	$57.59	10.872%	$63.8512	$63.85	$63.85	$63.90
Purchase #4	$217.53	3.769%	$225.7287	$225.73	$225.75	$225.70
Purchase #5	$119.29	6.651%	$127.224	$127.22	$127.20	$127.20
Purchase #6	$209.42	10.391%	$231.1808	$231.18	$231.20	$231.20
Purchase #7	$64.46	12.720%	$72.6593	$72.66	$72.65	$72.70
7 purchase totals =	$758.51		$820.0331	$820.03	$820.05	$820.00