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	$66.76	5.665%	$70.542	$70.54	$70.55	$70.50
Purchase #2	$112.53	7.315%	$120.7616	$120.76	$120.75	$120.80
Purchase #3	$58.56	11.719%	$65.4226	$65.42	$65.40	$65.40
Purchase #4	$134.37	9.676%	$147.3716	$147.37	$147.35	$147.40
Purchase #5	$35.78	4.667%	$37.4499	$37.45	$37.45	$37.40
Purchase #6	$70.55	3.191%	$72.8013	$72.80	$72.80	$72.80
Purchase #7	$162.31	7.843%	$175.04	$175.04	$175.05	$175.00
7 purchase totals =	$640.86		$689.3890	$689.38	$689.35	$689.30