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	$59.28	13.705%	$67.4043	$67.40	$67.40	$67.40
Purchase #2	$124.91	5.599%	$131.9037	$131.90	$131.90	$131.90
Purchase #3	$34.37	9.851%	$37.7558	$37.76	$37.75	$37.80
Purchase #4	$96.83	3.740%	$100.4514	$100.45	$100.45	$100.50
Purchase #5	$61.90	8.798%	$67.346	$67.35	$67.35	$67.30
Purchase #6	$173.36	3.835%	$180.0084	$180.01	$180.00	$180.00
Purchase #7	$33.66	7.355%	$36.1357	$36.14	$36.15	$36.10
7 purchase totals =	$584.31		$621.0053	$621.01	$621.00	$621.00