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	$114.36	12.260%	$128.3805	$128.38	$128.40	$128.40
Purchase #2	$243.92	4.367%	$254.572	$254.57	$254.55	$254.60
Purchase #3	$68.78	12.406%	$77.3128	$77.31	$77.30	$77.30
Purchase #4	$213.50	12.625%	$240.4544	$240.45	$240.45	$240.50
Purchase #5	$42.34	12.477%	$47.6228	$47.62	$47.60	$47.60
Purchase #6	$234.68	3.485%	$242.8586	$242.86	$242.85	$242.90
Purchase #7	$33.25	4.108%	$34.6159	$34.62	$34.60	$34.60
7 purchase totals =	$950.83		$1,025.8170	$1,025.81	$1,025.75	$1,025.90