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	$95.70	6.649%	$102.0631	$102.06	$102.05	$102.10
Purchase #2	$242.31	9.482%	$265.2858	$265.29	$265.30	$265.30
Purchase #3	$27.90	9.491%	$30.548	$30.55	$30.55	$30.50
Purchase #4	$220.56	4.549%	$230.5933	$230.59	$230.60	$230.60
Purchase #5	$75.81	12.868%	$85.5652	$85.57	$85.55	$85.60
Purchase #6	$229.71	9.139%	$250.7032	$250.70	$250.70	$250.70
Purchase #7	$38.55	10.274%	$42.5106	$42.51	$42.50	$42.50
7 purchase totals =	$930.54		$1,007.2692	$1,007.27	$1,007.25	$1,007.30