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	$131.46	6.107%	$139.4883	$139.49	$139.50	$139.50
Purchase #2	$98.56	7.819%	$106.2664	$106.27	$106.25	$106.30
Purchase #3	$239.82	10.264%	$264.4351	$264.44	$264.45	$264.40
Purchase #4	$248.84	9.105%	$271.4969	$271.50	$271.50	$271.50
Purchase #5	$120.53	8.748%	$131.074	$131.07	$131.05	$131.10
Purchase #6	$128.40	3.504%	$132.8991	$132.90	$132.90	$132.90
Purchase #7	$247.81	8.689%	$269.3422	$269.34	$269.35	$269.30
7 purchase totals =	$1,215.42		$1,315.0020	$1,315.01	$1,315.00	$1,315.00