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	$71.76	8.810%	$78.0821	$78.08	$78.10	$78.10
Purchase #2	$99.89	6.833%	$106.7155	$106.72	$106.70	$106.70
Purchase #3	$137.79	8.419%	$149.3905	$149.39	$149.40	$149.40
Purchase #4	$164.89	12.264%	$185.1121	$185.11	$185.10	$185.10
Purchase #5	$24.73	9.615%	$27.1078	$27.11	$27.10	$27.10
Purchase #6	$73.73	6.736%	$78.6965	$78.70	$78.70	$78.70
Purchase #7	$41.30	4.177%	$43.0251	$43.03	$43.05	$43.00
7 purchase totals =	$614.09		$668.1296	$668.14	$668.15	$668.10