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	$155.99	9.322%	$170.5314	$170.53	$170.55	$170.50
Purchase #2	$134.31	9.855%	$147.5463	$147.55	$147.55	$147.50
Purchase #3	$18.59	10.436%	$20.5301	$20.53	$20.55	$20.50
Purchase #4	$55.30	7.255%	$59.312	$59.31	$59.30	$59.30
Purchase #5	$91.37	5.715%	$96.5918	$96.59	$96.60	$96.60
Purchase #6	$86.98	7.410%	$93.4252	$93.43	$93.45	$93.40
Purchase #7	$32.59	9.386%	$35.6489	$35.65	$35.65	$35.60
7 purchase totals =	$575.13		$623.5857	$623.59	$623.65	$623.40