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	$133.90	7.791%	$144.3321	$144.33	$144.35	$144.30
Purchase #2	$216.49	12.441%	$243.4235	$243.42	$243.40	$243.40
Purchase #3	$200.95	10.848%	$222.7491	$222.75	$222.75	$222.70
Purchase #4	$248.31	8.279%	$268.8676	$268.87	$268.85	$268.90
Purchase #5	$148.89	4.839%	$156.0948	$156.09	$156.10	$156.10
Purchase #6	$114.60	11.207%	$127.4432	$127.44	$127.45	$127.40
Purchase #7	$16.88	13.723%	$19.1964	$19.20	$19.20	$19.20
7 purchase totals =	$1,080.02		$1,182.1067	$1,182.10	$1,182.10	$1,182.00