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	$239.97	12.612%	$270.235	$270.24	$270.25	$270.20
Purchase #2	$242.31	7.514%	$260.5172	$260.52	$260.50	$260.50
Purchase #3	$44.66	11.566%	$49.8254	$49.83	$49.85	$49.80
Purchase #4	$182.39	7.679%	$196.3957	$196.40	$196.40	$196.40
Purchase #5	$200.33	4.682%	$209.7095	$209.71	$209.70	$209.70
Purchase #6	$98.65	6.285%	$104.8502	$104.85	$104.85	$104.90
Purchase #7	$96.52	9.325%	$105.5205	$105.52	$105.50	$105.50
7 purchase totals =	$1,104.83		$1,197.0535	$1,197.07	$1,197.05	$1,197.00