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	$6.83	13.571%	$7.7569	$7.76	$7.75	$7.80
Purchase #2	$37.91	6.495%	$40.3723	$40.37	$40.35	$40.40
Purchase #3	$19.69	9.752%	$21.6102	$21.61	$21.60	$21.60
Purchase #4	$58.54	11.158%	$65.0719	$65.07	$65.05	$65.10
Purchase #5	$249.34	9.633%	$273.3589	$273.36	$273.35	$273.40
Purchase #6	$43.27	10.786%	$47.9371	$47.94	$47.95	$47.90
Purchase #7	$64.98	9.622%	$71.2324	$71.23	$71.25	$71.20
7 purchase totals =	$480.56		$527.3397	$527.34	$527.30	$527.40