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	$90.87	10.676%	$100.5713	$100.57	$100.55	$100.60
Purchase #2	$98.90	10.522%	$109.3063	$109.31	$109.30	$109.30
Purchase #3	$75.89	13.574%	$86.1913	$86.19	$86.20	$86.20
Purchase #4	$248.51	5.594%	$262.4116	$262.41	$262.40	$262.40
Purchase #5	$77.45	13.623%	$88.001	$88.00	$88.00	$88.00
Purchase #6	$103.74	6.184%	$110.1553	$110.16	$110.15	$110.20
Purchase #7	$49.93	5.226%	$52.5393	$52.54	$52.55	$52.50
7 purchase totals =	$745.29		$809.1761	$809.18	$809.15	$809.20