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	$217.86	9.343%	$238.2147	$238.21	$238.20	$238.20
Purchase #2	$84.85	5.339%	$89.3801	$89.38	$89.40	$89.40
Purchase #3	$49.93	12.290%	$56.0664	$56.07	$56.05	$56.10
Purchase #4	$184.55	5.804%	$195.2613	$195.26	$195.25	$195.30
Purchase #5	$55.55	10.500%	$61.3828	$61.38	$61.40	$61.40
Purchase #6	$106.86	13.109%	$120.8683	$120.87	$120.85	$120.90
Purchase #7	$63.53	5.527%	$67.0413	$67.04	$67.05	$67.00
7 purchase totals =	$763.13		$828.2149	$828.21	$828.20	$828.30