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	$38.43	11.357%	$42.7945	$42.79	$42.80	$42.80
Purchase #2	$70.27	12.152%	$78.8092	$78.81	$78.80	$78.80
Purchase #3	$166.62	9.251%	$182.034	$182.03	$182.05	$182.00
Purchase #4	$126.49	11.412%	$140.925	$140.93	$140.95	$140.90
Purchase #5	$27.44	12.504%	$30.8711	$30.87	$30.85	$30.90
Purchase #6	$225.98	7.363%	$242.6189	$242.62	$242.60	$242.60
Purchase #7	$62.41	7.773%	$67.2611	$67.26	$67.25	$67.30
7 purchase totals =	$717.64		$785.3138	$785.31	$785.30	$785.30