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	$182.28	3.734%	$189.0863	$189.09	$189.10	$189.10
Purchase #2	$30.96	6.631%	$33.013	$33.01	$33.00	$33.00
Purchase #3	$135.32	4.741%	$141.7355	$141.74	$141.75	$141.70
Purchase #4	$126.43	11.843%	$141.4031	$141.40	$141.40	$141.40
Purchase #5	$109.49	3.702%	$113.5433	$113.54	$113.55	$113.50
Purchase #6	$242.92	7.175%	$260.3495	$260.35	$260.35	$260.30
Purchase #7	$94.99	4.794%	$99.5438	$99.54	$99.55	$99.50
7 purchase totals =	$922.39		$978.6745	$978.67	$978.70	$978.50