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	$167.41	6.450%	$178.2079	$178.21	$178.20	$178.20
Purchase #2	$53.94	10.534%	$59.622	$59.62	$59.60	$59.60
Purchase #3	$247.39	10.484%	$273.3264	$273.33	$273.35	$273.30
Purchase #4	$33.55	13.633%	$38.1239	$38.12	$38.10	$38.10
Purchase #5	$73.32	8.204%	$79.3352	$79.34	$79.35	$79.30
Purchase #6	$169.83	12.610%	$191.2456	$191.25	$191.25	$191.20
Purchase #7	$28.28	4.498%	$29.552	$29.55	$29.55	$29.60
7 purchase totals =	$773.72		$849.4130	$849.42	$849.40	$849.30