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	$72.48	6.789%	$77.4007	$77.40	$77.40	$77.40
Purchase #2	$193.57	13.437%	$219.58	$219.58	$219.60	$219.60
Purchase #3	$243.55	6.431%	$259.2127	$259.21	$259.20	$259.20
Purchase #4	$96.86	8.873%	$105.4544	$105.45	$105.45	$105.50
Purchase #5	$30.91	9.781%	$33.9333	$33.93	$33.95	$33.90
Purchase #6	$72.82	11.158%	$80.9453	$80.95	$80.95	$80.90
Purchase #7	$227.42	5.590%	$240.1328	$240.13	$240.15	$240.10
7 purchase totals =	$937.61		$1,016.6592	$1,016.65	$1,016.70	$1,016.60