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	$74.78	8.129%	$80.8589	$80.86	$80.85	$80.90
Purchase #2	$142.45	9.849%	$156.4799	$156.48	$156.50	$156.50
Purchase #3	$182.77	9.840%	$200.7546	$200.75	$200.75	$200.80
Purchase #4	$186.86	6.333%	$198.6938	$198.69	$198.70	$198.70
Purchase #5	$165.71	8.678%	$180.0903	$180.09	$180.10	$180.10
Purchase #6	$74.55	7.703%	$80.2926	$80.29	$80.30	$80.30
Purchase #7	$135.39	11.325%	$150.7229	$150.72	$150.70	$150.70
7 purchase totals =	$962.51		$1,047.8930	$1,047.88	$1,047.90	$1,048.00