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	$75.88	10.827%	$84.0955	$84.10	$84.10	$84.10
Purchase #2	$191.40	13.497%	$217.2333	$217.23	$217.25	$217.20
Purchase #3	$38.38	8.770%	$41.7459	$41.75	$41.75	$41.70
Purchase #4	$66.42	3.738%	$68.9028	$68.90	$68.90	$68.90
Purchase #5	$227.89	12.118%	$255.5057	$255.51	$255.50	$255.50
Purchase #6	$134.53	13.402%	$152.5597	$152.56	$152.55	$152.60
Purchase #7	$65.37	10.157%	$72.0096	$72.01	$72.00	$72.00
7 purchase totals =	$799.87		$892.0525	$892.06	$892.05	$892.00