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	$94.74	5.488%	$99.9393	$99.94	$99.95	$99.90
Purchase #2	$145.47	13.684%	$165.3761	$165.38	$165.40	$165.40
Purchase #3	$47.70	12.566%	$53.694	$53.69	$53.70	$53.70
Purchase #4	$59.58	4.610%	$62.3266	$62.33	$62.35	$62.30
Purchase #5	$122.95	3.438%	$127.177	$127.18	$127.20	$127.20
Purchase #6	$168.60	7.558%	$181.3428	$181.34	$181.35	$181.30
Purchase #7	$136.82	10.759%	$151.5405	$151.54	$151.55	$151.50
7 purchase totals =	$775.86		$841.3963	$841.40	$841.50	$841.30