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	$113.58	12.445%	$127.715	$127.72	$127.70	$127.70
Purchase #2	$56.26	5.517%	$59.3639	$59.36	$59.35	$59.40
Purchase #3	$182.78	4.250%	$190.5482	$190.55	$190.55	$190.50
Purchase #4	$112.25	10.695%	$124.2551	$124.26	$124.25	$124.30
Purchase #5	$5.93	10.210%	$6.5355	$6.54	$6.55	$6.50
Purchase #6	$216.33	9.179%	$236.1869	$236.19	$236.20	$236.20
Purchase #7	$91.41	3.704%	$94.7958	$94.80	$94.80	$94.80
7 purchase totals =	$778.54		$839.4004	$839.42	$839.40	$839.40