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	$29.54	9.723%	$32.4122	$32.41	$32.40	$32.40
Purchase #2	$27.62	13.213%	$31.2694	$31.27	$31.25	$31.30
Purchase #3	$171.34	6.658%	$182.7478	$182.75	$182.75	$182.70
Purchase #4	$14.81	4.768%	$15.5161	$15.52	$15.50	$15.50
Purchase #5	$59.54	4.658%	$62.3134	$62.31	$62.30	$62.30
Purchase #6	$117.82	12.676%	$132.7549	$132.75	$132.75	$132.80
Purchase #7	$81.84	4.866%	$85.8223	$85.82	$85.80	$85.80
7 purchase totals =	$502.51		$542.8361	$542.83	$542.75	$542.80