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	$30.56	7.574%	$32.8746	$32.87	$32.85	$32.90
Purchase #2	$151.54	10.768%	$167.8578	$167.86	$167.85	$167.90
Purchase #3	$224.44	9.396%	$245.5284	$245.53	$245.55	$245.50
Purchase #4	$34.30	4.715%	$35.9172	$35.92	$35.90	$35.90
Purchase #5	$207.42	7.226%	$222.4082	$222.41	$222.40	$222.40
Purchase #6	$18.68	13.360%	$21.1756	$21.18	$21.20	$21.20
Purchase #7	$128.37	13.370%	$145.5331	$145.53	$145.55	$145.50
7 purchase totals =	$795.31		$871.2949	$871.30	$871.30	$871.30