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	$243.59	11.583%	$271.805	$271.81	$271.80	$271.80
Purchase #2	$98.92	6.534%	$105.3834	$105.38	$105.40	$105.40
Purchase #3	$139.98	5.289%	$147.3835	$147.38	$147.40	$147.40
Purchase #4	$200.69	9.327%	$219.4084	$219.41	$219.40	$219.40
Purchase #5	$82.60	8.634%	$89.7317	$89.73	$89.75	$89.70
Purchase #6	$99.97	6.503%	$106.471	$106.47	$106.45	$106.50
Purchase #7	$193.64	9.745%	$212.5102	$212.51	$212.50	$212.50
7 purchase totals =	$1,059.39		$1,152.6932	$1,152.69	$1,152.70	$1,152.70