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	$127.39	8.193%	$137.8271	$137.83	$137.85	$137.80
Purchase #2	$165.48	10.520%	$182.8885	$182.89	$182.90	$182.90
Purchase #3	$157.69	9.319%	$172.3851	$172.39	$172.40	$172.40
Purchase #4	$190.56	12.837%	$215.0222	$215.02	$215.00	$215.00
Purchase #5	$161.25	5.259%	$169.7301	$169.73	$169.75	$169.70
Purchase #6	$74.60	11.837%	$83.4304	$83.43	$83.45	$83.40
Purchase #7	$127.91	9.474%	$140.0282	$140.03	$140.05	$140.00
7 purchase totals =	$1,004.88		$1,101.3116	$1,101.32	$1,101.40	$1,101.20