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	$12.35	9.393%	$13.51	$13.51	$13.50	$13.50
Purchase #2	$44.88	10.272%	$49.4901	$49.49	$49.50	$49.50
Purchase #3	$153.32	4.700%	$160.526	$160.53	$160.55	$160.50
Purchase #4	$130.89	10.403%	$144.5065	$144.51	$144.50	$144.50
Purchase #5	$82.26	9.207%	$89.8337	$89.83	$89.85	$89.80
Purchase #6	$175.42	7.696%	$188.9203	$188.92	$188.90	$188.90
Purchase #7	$159.93	4.624%	$167.3252	$167.33	$167.35	$167.30
7 purchase totals =	$759.05		$814.1118	$814.12	$814.15	$814.00