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	$132.42	13.670%	$150.5218	$150.52	$150.50	$150.50
Purchase #2	$124.42	13.686%	$141.4481	$141.45	$141.45	$141.40
Purchase #3	$70.81	10.629%	$78.3364	$78.34	$78.35	$78.30
Purchase #4	$12.30	12.696%	$13.8616	$13.86	$13.85	$13.90
Purchase #5	$127.94	11.188%	$142.2539	$142.25	$142.25	$142.30
Purchase #6	$28.92	10.213%	$31.8736	$31.87	$31.85	$31.90
Purchase #7	$242.49	11.613%	$270.6504	$270.65	$270.65	$270.70
7 purchase totals =	$739.30		$828.9458	$828.94	$828.90	$829.00