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	$32.44	9.301%	$35.4572	$35.46	$35.45	$35.50
Purchase #2	$239.91	4.500%	$250.706	$250.71	$250.70	$250.70
Purchase #3	$177.45	4.258%	$185.0058	$185.01	$185.00	$185.00
Purchase #4	$24.98	13.399%	$28.3271	$28.33	$28.35	$28.30
Purchase #5	$217.60	4.719%	$227.8685	$227.87	$227.85	$227.90
Purchase #6	$72.60	11.353%	$80.8423	$80.84	$80.85	$80.80
Purchase #7	$27.89	10.678%	$30.8681	$30.87	$30.85	$30.90
7 purchase totals =	$792.87		$839.0750	$839.09	$839.05	$839.10