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	$31.38	12.736%	$35.3766	$35.38	$35.40	$35.40
Purchase #2	$231.78	10.711%	$256.606	$256.61	$256.60	$256.60
Purchase #3	$167.65	3.120%	$172.8807	$172.88	$172.90	$172.90
Purchase #4	$219.99	5.272%	$231.5879	$231.59	$231.60	$231.60
Purchase #5	$189.79	3.653%	$196.723	$196.72	$196.70	$196.70
Purchase #6	$223.46	13.314%	$253.2115	$253.21	$253.20	$253.20
Purchase #7	$159.85	3.467%	$165.392	$165.39	$165.40	$165.40
7 purchase totals =	$1,223.90		$1,311.7777	$1,311.78	$1,311.80	$1,311.80