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	$242.64	13.165%	$274.5836	$274.58	$274.60	$274.60
Purchase #2	$68.75	4.710%	$71.9881	$71.99	$72.00	$72.00
Purchase #3	$5.28	9.134%	$5.7623	$5.76	$5.75	$5.80
Purchase #4	$124.64	6.184%	$132.3477	$132.35	$132.35	$132.30
Purchase #5	$38.53	10.157%	$42.4435	$42.44	$42.45	$42.40
Purchase #6	$148.71	9.411%	$162.7051	$162.71	$162.70	$162.70
Purchase #7	$90.72	4.787%	$95.0628	$95.06	$95.05	$95.10
7 purchase totals =	$719.27		$784.8931	$784.89	$784.90	$784.90