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	$178.44	5.618%	$188.4648	$188.46	$188.45	$188.50
Purchase #2	$40.25	6.433%	$42.8393	$42.84	$42.85	$42.80
Purchase #3	$231.27	13.239%	$261.8878	$261.89	$261.90	$261.90
Purchase #4	$211.93	6.797%	$226.3349	$226.33	$226.35	$226.30
Purchase #5	$93.52	9.239%	$102.1603	$102.16	$102.15	$102.20
Purchase #6	$100.44	9.492%	$109.9738	$109.97	$109.95	$110.00
Purchase #7	$42.84	10.279%	$47.2435	$47.24	$47.25	$47.20
7 purchase totals =	$898.69		$978.9044	$978.89	$978.90	$978.90