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	$38.26	5.726%	$40.4508	$40.45	$40.45	$40.50
Purchase #2	$118.69	12.819%	$133.9049	$133.90	$133.90	$133.90
Purchase #3	$245.88	4.144%	$256.0693	$256.07	$256.05	$256.10
Purchase #4	$65.60	12.254%	$73.6386	$73.64	$73.65	$73.60
Purchase #5	$102.31	5.794%	$108.2378	$108.24	$108.25	$108.20
Purchase #6	$162.46	7.651%	$174.8898	$174.89	$174.90	$174.90
Purchase #7	$33.45	5.822%	$35.3975	$35.40	$35.40	$35.40
7 purchase totals =	$766.65		$822.5887	$822.59	$822.60	$822.60