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	$95.77	5.165%	$100.7165	$100.72	$100.70	$100.70
Purchase #2	$36.62	10.393%	$40.4259	$40.43	$40.45	$40.40
Purchase #3	$160.29	9.194%	$175.0271	$175.03	$175.05	$175.00
Purchase #4	$100.44	13.623%	$114.1229	$114.12	$114.10	$114.10
Purchase #5	$223.33	7.157%	$239.3137	$239.31	$239.30	$239.30
Purchase #6	$182.44	10.139%	$200.9376	$200.94	$200.95	$200.90
Purchase #7	$135.79	4.783%	$142.2848	$142.28	$142.30	$142.30
7 purchase totals =	$934.68		$1,012.8285	$1,012.83	$1,012.85	$1,012.70