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	$236.88	11.698%	$264.5902	$264.59	$264.60	$264.60
Purchase #2	$81.46	5.216%	$85.709	$85.71	$85.70	$85.70
Purchase #3	$226.36	7.286%	$242.8526	$242.85	$242.85	$242.90
Purchase #4	$12.59	4.710%	$13.183	$13.18	$13.20	$13.20
Purchase #5	$104.43	6.522%	$111.2409	$111.24	$111.25	$111.20
Purchase #6	$137.93	13.340%	$156.3299	$156.33	$156.35	$156.30
Purchase #7	$44.78	9.715%	$49.1304	$49.13	$49.15	$49.10
7 purchase totals =	$844.43		$923.0360	$923.03	$923.10	$923.00