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	$71.32	8.472%	$77.3622	$77.36	$77.35	$77.40
Purchase #2	$232.90	3.869%	$241.9109	$241.91	$241.90	$241.90
Purchase #3	$134.91	11.500%	$150.4247	$150.42	$150.40	$150.40
Purchase #4	$159.56	5.465%	$168.28	$168.28	$168.30	$168.30
Purchase #5	$169.81	9.803%	$186.4565	$186.46	$186.45	$186.50
Purchase #6	$33.76	10.544%	$37.3197	$37.32	$37.30	$37.30
Purchase #7	$15.76	12.346%	$17.7057	$17.71	$17.70	$17.70
7 purchase totals =	$818.02		$879.4597	$879.46	$879.40	$879.50