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	$14.84	5.662%	$15.6802	$15.68	$15.70	$15.70
Purchase #2	$127.84	11.216%	$142.1785	$142.18	$142.20	$142.20
Purchase #3	$71.82	11.480%	$80.0649	$80.06	$80.05	$80.10
Purchase #4	$175.96	7.776%	$189.6426	$189.64	$189.65	$189.60
Purchase #5	$119.56	6.498%	$127.329	$127.33	$127.35	$127.30
Purchase #6	$86.87	3.634%	$90.0269	$90.03	$90.05	$90.00
Purchase #7	$37.84	5.822%	$40.043	$40.04	$40.05	$40.00
7 purchase totals =	$634.73		$684.9651	$684.96	$685.05	$684.90