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	$141.37	10.564%	$156.3043	$156.30	$156.30	$156.30
Purchase #2	$99.74	12.536%	$112.2434	$112.24	$112.25	$112.20
Purchase #3	$85.59	4.448%	$89.397	$89.40	$89.40	$89.40
Purchase #4	$131.65	4.352%	$137.3794	$137.38	$137.40	$137.40
Purchase #5	$170.67	7.428%	$183.3474	$183.35	$183.35	$183.30
Purchase #6	$102.59	10.146%	$112.9988	$113.00	$113.00	$113.00
Purchase #7	$132.56	5.869%	$140.3399	$140.34	$140.35	$140.30
7 purchase totals =	$864.17		$932.0102	$932.01	$932.05	$931.90