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	$54.48	12.157%	$61.1031	$61.10	$61.10	$61.10
Purchase #2	$51.57	13.382%	$58.4711	$58.47	$58.45	$58.50
Purchase #3	$68.28	3.710%	$70.8132	$70.81	$70.80	$70.80
Purchase #4	$207.77	11.407%	$231.4703	$231.47	$231.45	$231.50
Purchase #5	$42.44	6.498%	$45.1978	$45.20	$45.20	$45.20
Purchase #6	$78.51	13.869%	$89.3986	$89.40	$89.40	$89.40
Purchase #7	$33.99	8.543%	$36.8938	$36.89	$36.90	$36.90
7 purchase totals =	$537.04		$593.3479	$593.34	$593.30	$593.40