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	$108.40	13.857%	$123.421	$123.42	$123.40	$123.40
Purchase #2	$32.56	8.840%	$35.4383	$35.44	$35.45	$35.40
Purchase #3	$133.52	8.551%	$144.9373	$144.94	$144.95	$144.90
Purchase #4	$241.88	10.498%	$267.2726	$267.27	$267.25	$267.30
Purchase #5	$246.50	9.417%	$269.7129	$269.71	$269.70	$269.70
Purchase #6	$13.88	9.816%	$15.2425	$15.24	$15.25	$15.20
Purchase #7	$16.78	10.736%	$18.5815	$18.58	$18.60	$18.60
7 purchase totals =	$793.52		$874.6061	$874.60	$874.60	$874.50