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	$82.98	9.518%	$90.878	$90.88	$90.90	$90.90
Purchase #2	$9.85	5.469%	$10.3887	$10.39	$10.40	$10.40
Purchase #3	$166.27	11.432%	$185.278	$185.28	$185.30	$185.30
Purchase #4	$14.59	6.434%	$15.5287	$15.53	$15.55	$15.50
Purchase #5	$140.76	7.487%	$151.2987	$151.30	$151.30	$151.30
Purchase #6	$140.99	6.768%	$150.5322	$150.53	$150.55	$150.50
Purchase #7	$147.65	5.814%	$156.2344	$156.23	$156.25	$156.20
7 purchase totals =	$703.09		$760.1387	$760.14	$760.25	$760.10