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	$156.38	10.142%	$172.2401	$172.24	$172.25	$172.20
Purchase #2	$7.53	4.301%	$7.8539	$7.85	$7.85	$7.90
Purchase #3	$85.89	5.242%	$90.3924	$90.39	$90.40	$90.40
Purchase #4	$163.68	12.603%	$184.3086	$184.31	$184.30	$184.30
Purchase #5	$74.59	8.674%	$81.0599	$81.06	$81.05	$81.10
Purchase #6	$82.53	9.416%	$90.301	$90.30	$90.30	$90.30
Purchase #7	$150.87	8.801%	$164.1481	$164.15	$164.15	$164.10
7 purchase totals =	$721.47		$790.3040	$790.30	$790.30	$790.30