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	$246.75	10.248%	$272.0369	$272.04	$272.05	$272.00
Purchase #2	$41.49	3.299%	$42.8588	$42.86	$42.85	$42.90
Purchase #3	$211.48	6.794%	$225.848	$225.85	$225.85	$225.80
Purchase #4	$209.47	10.717%	$231.9189	$231.92	$231.90	$231.90
Purchase #5	$11.29	4.695%	$11.8201	$11.82	$11.80	$11.80
Purchase #6	$209.93	11.689%	$234.4687	$234.47	$234.45	$234.50
Purchase #7	$42.31	12.735%	$47.6982	$47.70	$47.70	$47.70
7 purchase totals =	$972.72		$1,066.6496	$1,066.66	$1,066.60	$1,066.60