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	$39.68	9.216%	$43.3369	$43.34	$43.35	$43.30
Purchase #2	$132.37	11.268%	$147.2855	$147.29	$147.30	$147.30
Purchase #3	$170.59	8.586%	$185.2369	$185.24	$185.25	$185.20
Purchase #4	$153.79	6.869%	$164.3538	$164.35	$164.35	$164.40
Purchase #5	$177.32	6.214%	$188.3387	$188.34	$188.35	$188.30
Purchase #6	$98.82	10.841%	$109.5331	$109.53	$109.55	$109.50
Purchase #7	$65.83	4.219%	$68.6074	$68.61	$68.60	$68.60
7 purchase totals =	$838.40		$906.6923	$906.70	$906.75	$906.60