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	$33.62	11.458%	$37.4722	$37.47	$37.45	$37.50
Purchase #2	$45.31	4.533%	$47.3639	$47.36	$47.35	$47.40
Purchase #3	$108.64	12.707%	$122.4449	$122.44	$122.45	$122.40
Purchase #4	$235.31	4.490%	$245.8754	$245.88	$245.90	$245.90
Purchase #5	$127.45	13.691%	$144.8992	$144.90	$144.90	$144.90
Purchase #6	$63.74	12.704%	$71.8375	$71.84	$71.85	$71.80
Purchase #7	$132.71	11.770%	$148.33	$148.33	$148.35	$148.30
7 purchase totals =	$746.78		$818.2231	$818.22	$818.25	$818.20