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	$10.55	6.513%	$11.2371	$11.24	$11.25	$11.20
Purchase #2	$139.74	7.600%	$150.3602	$150.36	$150.35	$150.40
Purchase #3	$63.27	9.771%	$69.4521	$69.45	$69.45	$69.50
Purchase #4	$98.62	10.619%	$109.0925	$109.09	$109.10	$109.10
Purchase #5	$103.73	10.157%	$114.2659	$114.27	$114.25	$114.30
Purchase #6	$84.45	13.557%	$95.8989	$95.90	$95.90	$95.90
Purchase #7	$76.97	7.212%	$82.5211	$82.52	$82.50	$82.50
7 purchase totals =	$577.33		$632.8278	$632.83	$632.80	$632.90