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	$250.43	12.282%	$281.1878	$281.19	$281.20	$281.20
Purchase #2	$191.49	10.406%	$211.4164	$211.42	$211.40	$211.40
Purchase #3	$76.59	12.642%	$86.2725	$86.27	$86.25	$86.30
Purchase #4	$48.89	8.479%	$53.0354	$53.04	$53.05	$53.00
Purchase #5	$249.81	3.373%	$258.2361	$258.24	$258.25	$258.20
Purchase #6	$150.57	6.521%	$160.3887	$160.39	$160.40	$160.40
Purchase #7	$82.64	9.496%	$90.4875	$90.49	$90.50	$90.50
7 purchase totals =	$1,050.42		$1,141.0244	$1,141.04	$1,141.05	$1,141.00