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	$250.85	6.859%	$268.0558	$268.06	$268.05	$268.10
Purchase #2	$189.52	3.558%	$196.2631	$196.26	$196.25	$196.30
Purchase #3	$59.65	8.225%	$64.5562	$64.56	$64.55	$64.60
Purchase #4	$81.31	5.809%	$86.0333	$86.03	$86.05	$86.00
Purchase #5	$48.65	5.274%	$51.2158	$51.22	$51.20	$51.20
Purchase #6	$49.72	7.776%	$53.5862	$53.59	$53.60	$53.60
Purchase #7	$63.62	12.781%	$71.7513	$71.75	$71.75	$71.80
7 purchase totals =	$743.32		$791.4617	$791.47	$791.45	$791.60