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	$55.68	7.306%	$59.748	$59.75	$59.75	$59.70
Purchase #2	$231.42	3.751%	$240.1006	$240.10	$240.10	$240.10
Purchase #3	$98.86	4.849%	$103.6537	$103.65	$103.65	$103.70
Purchase #4	$225.44	11.582%	$251.5505	$251.55	$251.55	$251.60
Purchase #5	$224.71	7.619%	$241.8307	$241.83	$241.85	$241.80
Purchase #6	$27.27	4.370%	$28.4617	$28.46	$28.45	$28.50
Purchase #7	$44.83	8.165%	$48.4904	$48.49	$48.50	$48.50
7 purchase totals =	$908.21		$973.8356	$973.83	$973.85	$973.90