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	$236.46	12.570%	$266.183	$266.18	$266.20	$266.20
Purchase #2	$187.77	6.736%	$200.4182	$200.42	$200.40	$200.40
Purchase #3	$213.98	10.313%	$236.0478	$236.05	$236.05	$236.00
Purchase #4	$152.85	7.385%	$164.138	$164.14	$164.15	$164.10
Purchase #5	$250.52	9.463%	$274.2267	$274.23	$274.25	$274.20
Purchase #6	$68.27	6.582%	$72.7635	$72.76	$72.75	$72.80
Purchase #7	$130.57	11.396%	$145.4498	$145.45	$145.45	$145.40
7 purchase totals =	$1,240.42		$1,359.2270	$1,359.23	$1,359.25	$1,359.10