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	$92.40	5.507%	$97.4885	$97.49	$97.50	$97.50
Purchase #2	$99.96	9.289%	$109.2453	$109.25	$109.25	$109.20
Purchase #3	$28.56	9.838%	$31.3697	$31.37	$31.35	$31.40
Purchase #4	$140.41	10.712%	$155.4507	$155.45	$155.45	$155.50
Purchase #5	$54.75	12.362%	$61.5182	$61.52	$61.50	$61.50
Purchase #6	$143.36	7.808%	$154.5535	$154.55	$154.55	$154.60
Purchase #7	$20.45	8.758%	$22.241	$22.24	$22.25	$22.20
7 purchase totals =	$579.89		$631.8669	$631.87	$631.85	$631.90