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	$74.85	4.258%	$78.0371	$78.04	$78.05	$78.00
Purchase #2	$124.67	6.604%	$132.9032	$132.90	$132.90	$132.90
Purchase #3	$63.32	3.515%	$65.5457	$65.55	$65.55	$65.50
Purchase #4	$127.45	11.538%	$142.1552	$142.16	$142.15	$142.20
Purchase #5	$19.96	4.160%	$20.7903	$20.79	$20.80	$20.80
Purchase #6	$50.44	10.241%	$55.6056	$55.61	$55.60	$55.60
Purchase #7	$35.37	10.300%	$39.0131	$39.01	$39.00	$39.00
7 purchase totals =	$496.06		$534.0502	$534.06	$534.05	$534.00