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	$84.45	7.151%	$90.489	$90.49	$90.50	$90.50
Purchase #2	$171.38	5.672%	$181.1007	$181.10	$181.10	$181.10
Purchase #3	$59.88	11.475%	$66.7512	$66.75	$66.75	$66.80
Purchase #4	$78.78	4.655%	$82.4472	$82.45	$82.45	$82.40
Purchase #5	$24.75	8.383%	$26.8248	$26.82	$26.80	$26.80
Purchase #6	$197.69	7.491%	$212.499	$212.50	$212.50	$212.50
Purchase #7	$245.95	12.786%	$277.3972	$277.40	$277.40	$277.40
7 purchase totals =	$862.88		$937.5091	$937.51	$937.50	$937.50