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	$230.78	13.275%	$261.416	$261.42	$261.40	$261.40
Purchase #2	$206.61	10.511%	$228.3268	$228.33	$228.35	$228.30
Purchase #3	$127.40	5.330%	$134.1904	$134.19	$134.20	$134.20
Purchase #4	$137.52	6.417%	$146.3447	$146.34	$146.35	$146.30
Purchase #5	$90.51	12.223%	$101.573	$101.57	$101.55	$101.60
Purchase #6	$71.31	9.835%	$78.3233	$78.32	$78.30	$78.30
Purchase #7	$102.83	7.713%	$110.7613	$110.76	$110.75	$110.80
7 purchase totals =	$966.96		$1,060.9355	$1,060.93	$1,060.90	$1,060.90