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	$135.55	12.499%	$152.4924	$152.49	$152.50	$152.50
Purchase #2	$56.72	5.406%	$59.7863	$59.79	$59.80	$59.80
Purchase #3	$34.51	11.600%	$38.5132	$38.51	$38.50	$38.50
Purchase #4	$139.66	12.523%	$157.1496	$157.15	$157.15	$157.10
Purchase #5	$239.52	12.503%	$269.4672	$269.47	$269.45	$269.50
Purchase #6	$160.66	8.560%	$174.4125	$174.41	$174.40	$174.40
Purchase #7	$165.56	6.720%	$176.6856	$176.69	$176.70	$176.70
7 purchase totals =	$932.18		$1,028.5068	$1,028.51	$1,028.50	$1,028.50