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	$120.31	3.370%	$124.3644	$124.36	$124.35	$124.40
Purchase #2	$74.48	8.144%	$80.5457	$80.55	$80.55	$80.50
Purchase #3	$131.65	5.765%	$139.2396	$139.24	$139.25	$139.20
Purchase #4	$91.31	13.150%	$103.3173	$103.32	$103.30	$103.30
Purchase #5	$245.39	5.499%	$258.884	$258.88	$258.90	$258.90
Purchase #6	$150.58	6.612%	$160.5363	$160.54	$160.55	$160.50
Purchase #7	$115.53	6.709%	$123.2809	$123.28	$123.30	$123.30
7 purchase totals =	$929.25		$990.1682	$990.17	$990.20	$990.10