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	$188.95	4.132%	$196.7574	$196.76	$196.75	$196.80
Purchase #2	$89.40	7.404%	$96.0192	$96.02	$96.00	$96.00
Purchase #3	$241.70	13.552%	$274.4552	$274.46	$274.45	$274.50
Purchase #4	$95.92	6.768%	$102.4119	$102.41	$102.40	$102.40
Purchase #5	$91.82	9.575%	$100.6118	$100.61	$100.60	$100.60
Purchase #6	$70.36	13.828%	$80.0894	$80.09	$80.10	$80.10
Purchase #7	$96.94	13.398%	$109.928	$109.93	$109.95	$109.90
7 purchase totals =	$875.09		$960.2729	$960.28	$960.25	$960.30