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	$104.25	7.289%	$111.8488	$111.85	$111.85	$111.80
Purchase #2	$51.48	11.142%	$57.2159	$57.22	$57.20	$57.20
Purchase #3	$191.39	9.349%	$209.2831	$209.28	$209.30	$209.30
Purchase #4	$109.28	6.731%	$116.6356	$116.64	$116.65	$116.60
Purchase #5	$122.88	13.123%	$139.0055	$139.01	$139.00	$139.00
Purchase #6	$120.96	7.551%	$130.0937	$130.09	$130.10	$130.10
Purchase #7	$51.77	13.442%	$58.7289	$58.73	$58.75	$58.70
7 purchase totals =	$752.01		$822.8115	$822.82	$822.85	$822.70