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	$29.63	12.383%	$33.2991	$33.30	$33.30	$33.30
Purchase #2	$239.27	3.445%	$247.5129	$247.51	$247.50	$247.50
Purchase #3	$103.83	12.145%	$116.4402	$116.44	$116.45	$116.40
Purchase #4	$51.95	11.321%	$57.8313	$57.83	$57.85	$57.80
Purchase #5	$23.76	7.327%	$25.5009	$25.50	$25.50	$25.50
Purchase #6	$79.37	4.652%	$83.0623	$83.06	$83.05	$83.10
Purchase #7	$225.31	3.803%	$233.8785	$233.88	$233.90	$233.90
7 purchase totals =	$753.12		$797.5252	$797.52	$797.55	$797.50