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	$124.64	8.222%	$134.8879	$134.89	$134.90	$134.90
Purchase #2	$100.79	13.162%	$114.056	$114.06	$114.05	$114.10
Purchase #3	$232.39	7.686%	$250.2515	$250.25	$250.25	$250.30
Purchase #4	$23.76	10.323%	$26.2127	$26.21	$26.20	$26.20
Purchase #5	$103.52	12.730%	$116.6981	$116.70	$116.70	$116.70
Purchase #6	$96.33	9.279%	$105.2685	$105.27	$105.25	$105.30
Purchase #7	$72.38	13.144%	$81.8936	$81.89	$81.90	$81.90
7 purchase totals =	$753.81		$829.2683	$829.27	$829.25	$829.40